stop valve

hi, what options do i have to stop water flowing? i am trying to remove a shower, and this is the feed to it, the stop valve on the bottom pipe wont turn so need to know what I can do here please

Hey! Would anyone have any tips and guidance to fit this stop valve onto this pipe, please? It is a valve for a shower spray and i’m wanting it to go right in so the chrome plate covers the tile. I’m aware that something may need to go behind the tile so anything to make that simpler would be...