What to do if you forgot ur iPhone passcode

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

you will have to

connect it by the cable to a computer and read

If you forgot your iPad passcode - Apple Support