1. First of all, you can get name tags from the boxes in the dungeon, and there is also a certain probability of getting name tags when fishing.
2. Secondly, making a nameplate requires an anvil. The anvil needs to be synthesized using three iron blocks and four iron ingots.
3. Finally, right-click the anvil and place the name tag in the first grid. Click on the name bar above to change the name of my partner.