Is there a simple explanation on how to do that or can I find it somewhere else?
The patreon build is a build that's in development so there will be changes to the database (character balancing, new enemies, items etc.) so older saves won't 100% work on newer builds. I always make a pre-played save in each build to make it easier for my supporters to check out the new content. I know it sucks, but that's how game development with this engine works.