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 datapack adds compatibility with armor tiers of RPG Series mods and MC Dungeons Armors, making MCDA armors become an upgrade tier from the RPG Series armors.
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.