Here are some things that you need to do:
- Open the TestMod file and on the right side, find the PrimalGameDataOverride. Set that to your PrimalGameData file.
- What you have done is created a new berry, not modified the older one. You’ll have to replace the existing amarberry in your PrimalGameData with your PrimalItem.
These are the very basic steps, but after that you will need to copy a few more files into your mod folder to allow it to work.