Hi.
Just type in YouTube “a31 glass replacement” and there will be a lot of videos how doing this.
Please note - I'm doing this professionally so I have to tell You this: If You don't have proper equipment You’ll destroy the screen 95% doing this by Yourself.
If You don't have the machines to do this 100% by yourself - better buy new or refurbished screen and sell this one working cracked screen. Swapping whole screen is a lot easier than changing glass only.
Cheers!