I only recently noticed the bow of my SSD is curved upward and it really bothers me. I believe it came this way but I never noticed before but once seen it cannot be unseen.

When I press down on the affected section it goes into the correct allignment but obviously igoes back to being crooked the moment I release.

How can I fix this? Hairdryer, press down, and then let it cool?

(It looks much more curved up in person than photos seem to convey)

It begins to curve up around where my thumb and middle finger are gripping it.

Any help would be much appreciated.

One method I've used with some success on much smaller plastic models, is to dip the affected part into boiling water for just a few seconds, and then hold it in shape until it cools off.
Works better on softer plastics, so attempt at your own risk.

I would start with a hair dryer, and some rubber bands. You may need to build a frame to give you the propper tension points. Apply tension to just beyond straight. Apply heat across the bend evenly. It may take several attempts to relax the offending part.

I had the same issue with a 2 part shapeways SSD. Only one side had the hogging.

You could also try taking it apart to see what side has the issue. That would at least tell you what side needs to be relaxed with heat.