It's super easy, just download and put the "PRYDE x Plumfruit" folder in your mods folder! That's it! (make sure to unzip the folder first if you are using the unmerged version!)
The Install Directory is usually locatd under:
Make sure you have enabled Mods in your game’s settings! Go to settings/other and check the little boxes “enable custom content” and “enable script mods”