Backing up a broken iPhone 8

Ok so here's my problem,

I've had an iPhone 8 for just under 3 years now but the screen got very damaged recently so I can't click anything anymore and the screen sometimes presses random buttons on its own. I was away when it happened so I couldn't back it up straight away and it ran out of power between then and now. This means I need to type my password to do anything like use siri or use any accessories like a lightning keyboard which I thought i could use to type my password. The last back up I have is from around a yer ago so it already trusts the computer but i cant do it straight after a restart I still need to type the password one time first. I now have an iPhone SE which is signed into the same iCloud and I have moved my sim card over. I can see small slivers on the screen so I can see the start of notifications and then the rest is obvious like there is no sim in the phone or unlock iPhone to use accessories. Any suggestions?