To add to Justin's excellent answer, if you prefer the iFixit-style step by step instruction format, there's a Spanish site called Nadie Me Llama Gallina that has a screen replacement guide for your phone.
[link|https://www.nadiemellamagallina.com/en/manuales/smartphones-1/xiaomi-191/xiaomi-redmi-9-1289/pantalla-completa-11486|Manuales / Xiaomi Redmi 9 / Full screen|new_window=true]