Hallo friend
So a few things and I’ll assume some here to try and make it easy peasy!
1) you’ll need to be working with a windows or Mac computer
2) make sure the computer is fully up to date
3) if macOS 10.14.x or earlier or windows 10/8/7 make sure iTunes is installed and fully up to date (apple software update on pc)
4) place device into recovery mode link: https://support.apple.com/en-us/HT201263
5) if you have download issues make sure you’re not utilizing VPN or security software
6) launch iTunes it should prompt you — restore is full wipe, update attempts to save data
7) wait a while
8) setup phone when it says hello on a white display: https://support.apple.com/en-us/HT202033
hope this helps