The solution is often a fresh start using the (also known as the Stock Firmware or ROM).
Is your Redmi 7a stuck in a boot loop? Laggy? Hanging on the Mi Logo? Or maybe you forgot the screen lock password.
Redmi 7a Flash File: Download Official Firmware (Stock ROM) & Guide
Extract the Flash File ( .tgz ) using WinRAR or 7-Zip. You should get a folder with a name ending in _images .