THIS IS A DATAPACK! You need to either add it to your world's datapack folder or use an automatic loader such as OpenLoader or Paxi.
This simple datapack adds a recipe for Soul Stone from Bygone Nether. This block is required to summon the wither instead of soul sand, and a lot of players don't like the fact that they have to go to the nether to find this specific block. So as a solution this makes it craftable using 1 Soul Sand and 1 Soul Soil!
How to install?
Download the zip and put it in your world's datapacks folder.
Alternatively, install openloader or paxi, and put the datapack inside their data folder.