1. download and install UE 5.3 from Epic Games
2. create a blank project in that UE 5.3
3. download the content from Fab and add it to that blank project
4. inside UE 5.3, migrate the assets you want to use inside a new folder at the root of the project (I called it AAA_Th3, any name should work as long as it's not already in use by FactoryGame)
5. in Windows File Explorer, copy the AAA_Th3 folder from the blank project to the modding project
6. open the modding project in UE-CSS and move the AAA_Th3 folder from Content into the plugin (mod) of your choice
you can use the Epic Game store injust click add to project on the asset then clickUnreal Engine -> Libraryclick on the FactoryGame project it will come up with an error about not being compatible, just change the version to 5.3 and clickShow All Projectsadd to project