Start the game once (This should add more Folders inside the BepInEx Folder located in the Game folder)
Copy the randomizer dll into BepInEx/plugins
Start Tunic again and start a new game
Useful hints
Randomization does NOT prevent softlocks as of yet. Use Keyboard Button [I] to spawn bombs if you are stuck at the beginning (with the cost of half of your HP :P).
If you are stuck inside a level with no way out press Left-ALT followed by 0 and then again LEFT-ALT. This will warp you to the first entrance. If you want you can use other numbers to travel to other level exits if you so choose.
Use Keyboard Button T to look up your current Seed.
You can also use Keyboard Button N to switch between night and daytime.
Future improvements and bugfixes planned
Use of custom seeds
Save randomization settings and progress (right now the item randomizer does not work with save files at all)
Progression based randomization
Different randomization options (Like which item types to randomize, locking abilities (e.g. Praying and Rolling) behind a chest, ...)
Maybe locking abilities behind the page that initially teaches you about one would be a good starting point? i.e. you need the page normally inside the Sealed Temple in order to Pray at all