Sorry if this is a simple question, but if a minion or rival enemy rolls one threat, what do you do with it?

Sometimes, the minion/rival doesn't have some pre-existing bonus (such as being in cover, or guard stance or aim maneuver) which is what the rule book suggests to cancel, so can you use this 1 threat to give them one strain, but as they don't have strain thresholds, it turns into a wound instead?

I'd say take a look at the Core rulebook. If this is a combat situation I'd feel justified in giving the PC a boost die or giving the minion's next ally a setback die. Strain...maybe, but as a personal matter I'd prefer to give some advantage to the PCs. The minion shoots, but has to step away from cover a bit to do it. Or the minion gives away his position by firing at you, or knocks over a crate or something similar.

For a minion I typically take off a wound since strain is coverted to wounds. Minions are typically story road bumps so taking off 1 wound isn't breaking the narrative.

As you've noticed one Threat really has no value on the chart (it takes two to affect a PC or to give a Boost to another NPC) two is just the threshold for it to be a penalty. I don't have a problem with this and so I usually ignore it mechanically and use it to describe something in the combat.

I'd say take a look at the Core rulebook. If this is a combat situation I'd feel justified in giving the PC a boost die or giving the minion's next ally a setback die. Strain...maybe, but as a personal matter I'd prefer to give some advantage to the PCs. The minion shoots, but has to step away from cover a bit to do it. Or the minion gives away his position by firing at you, or knocks over a crate or something similar.

In the rules, it suggests a setback only on two threat (which is different to being able to have a boost to next ally with just 1 advantage)

As you've noticed one Threat really has no value on the chart (it takes two to affect a PC or to give a Boost to another NPC) two is just the threshold for it to be a penalty. I don't have a problem with this and so I usually ignore it mechanically and use it to describe something in the combat.

Yeah, in the chart it doesn't give much idea what to do with the just one threat. Which is why I was wondering if its not too powerful to give the NPC's one strain which converts to damage.

It's just hard when the players are all looking at me wondering what bad thing is going to happen, and i can't think of anything mechanically hopefully I can gloss over it with some fluffy piece of action then as you have suggested

I've used "stress of trying to shoot you caused him to..." And then I've filled in various things. Break out into a sweat, bump his head, shoot himself by mistake, and the gun exploding when it killed him.

Yeah, in the chart it doesn't give much idea what to do with the just one threat. Which is why I was wondering if its not too powerful to give the NPC's one strain which converts to damage.

It's just hard when the players are all looking at me wondering what bad thing is going to happen, and i can't think of anything mechanically hopefully I can gloss over it with some fluffy piece of action then as you have suggested

A single Threat isn't supposed to have a mechanical effect, one too easy to get, and it works the same for the PCs so I'd not give the Strain unless the PCs want it too, which I doubt. Just explain it as two is the threshold for badness that has an actual die or stat effect. Plus you don't have to describe everything, let them do it!

I give them a wound (as Strain). Describe it in a way that makes the Players feel good about the situation. "He gets the shot off, but your constant barrage of fire obviously has him shaken."

Players find it satisfying to see NPC's moving closer to being taken out.

On the flip side, I usually give PC's Strain if they roll one threat and I can't come up with any other quick thing. Watching their Strain drain away from the stress of the situation makes the combat dramatic.

I give them a wound (as Strain). Describe it in a way that makes the Players feel good about the situation. "He gets the shot off, but your constant barrage of fire obviously has him shaken."

Players find it satisfying to see NPC's moving closer to being taken out.

On the flip side, I usually give PC's Strain if they roll one threat and I can't come up with any other quick thing. Watching their Strain drain away from the stress of the situation makes the combat dramatic.

Same