Your best bet is to still probably try to take it apart. Usually more dedicated people cut the pegs on their kits to make them easier to take apart and do practice assembly runs before actually putting it together.
The most common methods for getting rid of seams and joining two pieces together is with welding glue that will melt the two pieces together. The other option would be putty, which you would have to paint as the color wouldn't match up.
You probably don't want to heat the plastic as it would burn, melt improperly, and might damage whatever it is you are using to heat it.
depending on how snugly that clear piece goes into it, you could try prying it out with a needle. if you're afraid that might scratch up the plastic, an alternative is to drill a hole from behind and push out the piece that way, since any hole you're making is gonna be covered by the seal anyways.
apparently there are suction cups for contact lenses? maybe give that a try too.
Thank you guys. I think making a hole behind is the best idea, I'll try that
I finished basic assembly but I need to buy something to put the really little decals. No painting or anything for me, I'm pretty happy with the thing as it is.