why do you want him to be a him
it's not like you want a relationship with him (or do you i don't think you can have a relationship with him but what do i know i never played a female character in the crpg's)

But ehm.... maybe you could try to remove his curse (donno if thats possible but just try it)
The only girdle of gender i ever for was near the friendly arm inn but that's in bg1

I left the underdark and Edwin and his nether scroll got themselves into a pickle! Now he's a she- and I need to find the girdle of gender. Can anyone tell me where it is- or if there is something else I should do? Thanks!

Get your mind out of the gutter, fool. There's no girdle of gender-changing in the game. The only way Edwin goes back to normal is with time.