Did you not ask CSI for a one click-fix. 
Every operating system listed but no mention of the version of Gimp you are using. Best demonstrated in Gimp 2.10
Your blank form is smaller in pixel size to the filled in form. You will need to scale it up. You could do that by eye, but a bit of measuring gives a scale factor of 186.82%. Then what do you do with it? Selection & cut can remove the white. Selection inverted and grown can replace the blue with something more solid and allow some overlap. That gave me a less-than-wonderful overlay. attached for you to play with. Put it on top and set the layer mode to erase.
Other ways? Colors -> Map -> Color Exchange easier to show in Gimp 2.10 than Gimp 2.8
![[Image: W7XBARn.jpg]](https://i.imgur.com/W7XBARn.jpg)
and a little 2 minute video demo, both overlay and color exchange: https://youtu.be/3foMwWWAUYo
Every operating system listed but no mention of the version of Gimp you are using. Best demonstrated in Gimp 2.10Your blank form is smaller in pixel size to the filled in form. You will need to scale it up. You could do that by eye, but a bit of measuring gives a scale factor of 186.82%. Then what do you do with it? Selection & cut can remove the white. Selection inverted and grown can replace the blue with something more solid and allow some overlap. That gave me a less-than-wonderful overlay. attached for you to play with. Put it on top and set the layer mode to erase.
Other ways? Colors -> Map -> Color Exchange easier to show in Gimp 2.10 than Gimp 2.8
and a little 2 minute video demo, both overlay and color exchange: https://youtu.be/3foMwWWAUYo