How can I change the display

Sorry to say, iFixit being primarily an American company, is light on European phones like the Xiaomi line and as such doesn't have a guide for your phone. There is, however, a Spanish site called Nadie Me Llama Gallina that has exactly what you need.

Manuales / Xiaomi Redmi 7 / screen - Nadie Me Llama Gallina

The site is, as you might guess, written in Spanish, but if you use it together with the Chrome browser's translation feature, then it becomes quite usable no matter what your native language is. I've found the guides to be well done and complete, so I'm confident you will be able to fix your phone with this one.

As you work, take lots of pictures and once. you're done you can use them to create your own iFixit guide to that repair for those who come after you with the same problem. It's easy, fun and will earn the appreciation of the repair community.

Unfortunately, the Nadie Me Llama Gallina site appears to have been taken over and taken down, so the previous link to their repair guide is no longer usable.

I've located another guide to screen replacement on the French site SOSav. Like the Spanish site I cited earlier, it's not in English, but again, the use of a browser that does translation makes the guide usable no matter what your native language is.

Xiaomi Redmi 7 Screen Repair - Free Guide - SOSav.fr

This guide assumes you are doing a screen+frame replacement, which is the safest way and is usually recommended (that's where you buy the screen already attached to the midframe and transfer the internals of your phone to the new assembly). You can find screen only replacement guides on YouTube if you prefer that method.