I forgot screen passcode

I need to change screen passcode

To do that, you first need to erase / reset your phone so all the data on your phone will be lost. Then, set it up again.

If you have a current backup of the phone, you can use that to restore data back to the phone after it has been set up again.

See.....If you forgot your iPhone passcode - Apple Support

See this for a forgotten passcode. If you forgot your iPhone passcode - Apple Support