Netherite

You need a smithing table.

You need to gather 4 ancient debris to smelt into netherite scrap to craft with 4 gold which makes one netherrite ingot. Which then can be used in a smithing table to upgrade existing diamond gear

https://minecraft.gamepedia.com/Netherite

Cleaning up old tickets: This ticket had been set to 'Awaiting Response', but has not received a response from the reporter (~3 months+) so is being closed as Incomplete. If you feel this is still a valid issue then please comment, or create a new ticket following the Issue Guidelines which includes steps to reproduce the problem.

Quick Links:
📓 Issue Guidelines – 💬 Mojang Support – 📧 Suggestions – 📖 Minecraft Wiki

Are you using an anvil or a crafting table? If yes, you need to use a smithing table to smith a netherite ingot to a diamond gear like this: