Follow instructions on this link. First update the phone to the latest MIUI 12.5 version and then type "Redmi 9T update tracker" in google and open xda developer site, choose and download two recovery Roms, one you already have ( the latest) and one you want - lets say MIUI 12.0.10. (DONT YOU DOWNLOAD FIRST VERSIONS OF MIUI 12 LIKE MIUI 12.01 OR MIUI 12.02, YOU CAN BRICK THE PHONE. ONLY FROM MIUI 12.08 AND UPPER. MIUI 12.0.10 IS THE BEST I THINK)
After you download them, follow the instructions about update with renaming the MIUI and you will do it.