another way
I am never sure which version of Gimp you use

Last definitive post seemed to be Gimp 2.10. in Win10 Home. But since then, might be either Parthas version or Samj's portable.
Assuming regular Gimp 2.10
You could add a right-click context menu item specifically opening a file in Gimp.
Something like this: Before

and with an added menu item

You need to create a something.reg file to add the entry.
This one for a regular Gimp 2.10 installation The path needs to be edited for anything else.
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Edit with GIMP]
[HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Edit with GIMP\command]
@="\"C:\\Program Files\\GIMP 2\\bin\\gimp-2.10.exe\" \"%1\""
and if you ever need to remove it
Windows Registry Editor Version 5.00
[-HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Edit with GIMP]
[-HKEY_CLASSES_ROOT\SystemFileAssociations\image\shell\Edit with GIMP\command]
@="\"C:\\Program Files\\GIMP 2\\bin\\gimp-2.10.exe\" \"%1\""
zipped and attached the two files: unzip, click on the file to start, ok all the dire warnings Windows throws at you.