How do I fix a phone that is unavailable

If you forgot a passcode that you changed within the last 72 hours, see the following for instructions: Temporarily use your old passcode when you forget your new passcode on iPhone or iPad - Apple Support

Otherwise, there is an Apple article that explains what to do if you have forgotten an iPhone or iPad passcode. Click on the following link: If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

If that is not an option, you will need to use a computer. See:

If you forgot your iPhone passcode - Apple Support

or

If you forgot your iPad passcode - Apple Support

Click on the blue links for instructions.

Start with: If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

If that doesn't help, you will need to use a computer and the instructions in If you forgot your iPhone passcode - Apple Support

You follow the instructions that FoxFifth provided you.