Apple

Hello today i got my hands on a iphone 15 256gb at home i charged it and then startet it i tried to set it up and came to the part were you Design if you want to a SoftwareUpdate or yoj do it later i did it and now i'm kinda stuck in the loading screen of the Software Update i can't go back i cant turn it off completly just on and off i cant go in the settings and the real problem is that it doesnt load not like slow more like there is no blue line(nothing) if someone knows how to shuttle the phone off it would really helpdesk me(i don't want to make the Batterie go to 0%) since i am Android i don't know how to shut a iphone down other than Pressung the on/of Button for a few second. Pls help me (enlgish is not my first langugage)