Updating a mod's source code for a newer forge version

[BobbyKilkins]

Recently I stumbled upon an old private mod project I made for 1.7.10. It still works and everything, and I would like to update it to 1.12.2, since it seems like the main modding version currently. I want to use it in a new modpack playthrough on 1.12.2. I obviously still have the source code; How can I update it without rewriting it? How hard/easy will it be? Should I just add 1.12.2 forge to the eclipse project and go around trying to fix the red squiggly lines?

Thanks for your time 

[Luis_ST]

1.12 is no longer supported on this forum.

Please update to a modern version of Minecraft to receive support.