The battery is dead

Sorry to say iFixit doesn't have a guide for the repair you need, but the Spanish site Nadie Me Llama Gallina (Nobody Calls Me Chicken) has exactly what you're looking for. The guide is, of course, written in Spanish, but used with the Chrome browser's translation feature, it is quite usable no matter what your native language is.

Manuales / Realme 6 / Drums - Nadie Me Llama Gallina

There is an oddity in the translation to English that will make it easier to understand if you know about it. For some reason the term Battery comes through as Drums in the web page, but comes through correctly in the instructions. Otherwise their guides are well written and complete.

Of course, as long as you're doing the work anyway, why don't you go ahead and take lots of pictures as you work, then you can use them to create your own iFixit guide for those who come after you. It's easy, fun, and you'll have the gratitude of the repair community.

Create a new Guide - iFixit