If you can still access your old save files from the Itch app then you just have to copy the save files into your game folder. It's usually this directory: D:\Program (or wherever you installed your Itch app program)\Itch\Games\our-life\OurLife-1.1-pc\game and there you should put your old save files (just copy/paste the saves folder).
If you don't use the itch app than it's probably somewhere in your appdata files. Usually C:\Users\PC\AppData\Roaming\Renpy\Our Life\
I hope this helps.