Problem with necessary backup before sending away for repair

Thanks Bob for your reply & by pure fluke came up with what you suggested & connected it to my MacBook. Now my problem is that I can't empty the phone to send for repair. It won't led me turn off "Find My" as it won't connect to the net, exactly the same when I want to disconnect it from iCloud. I bought a little cheap phone just for basic calls if main phone is away or not working and was hugely relieved when it arrived. Now I just don't know what to do next as my iPhone still contains everything that was on it & I don't want to send it away like that. Bob, I would be very grateful if you or anyone else have any further words of wisdom to prevent the phone from hitting the wall, I've been trying everything on Youtube & more for almost a fortnight now so feeling rather frustrated by it all. Thank you in advance to anyone who takes time to post suggestions 😎