my iphone xr is continually booting to the homescreen and then switiching off and restarting, any ideas how to fix this?

Try a forced restart. First take off any case. Then:

Press and very quickly release the volume up button. > Immediately press and very quickly release by the volume down button > Immediately press and hold down the side button and keep holding the side button until the Apple logo appears, release the side button. If your iPhone won't turn on or is frozen - Apple Support