How to replace volume button

Are you referring to the external, physical button or the internal circuit board with the metal domes that the outside button presses to activate? This guide shows how to replace the internal power/volume button flex cable.

Redmi Note 10 Power and Volume Flex Cable Repair - Free Guide - SOSav.fr

If it's an issue with the external button, I'm not sure if you can buy it separately, but it will come with a replacement midframe, the part that includes the fingerprint sensor. This guide shows how to replace that part.

Redmi Note 10 Fingerprint Sensor and Internal Frame Repair - Free Guide - SOSav.fr

The site is written in French, but used with a browser like Chrome that does translation, it is quite usable no matter what your native language is.

Good luck, and be sure to come back and let us know what you find. Your learning will help the next person who comes along with the same problem.