forgot passcode to unlock iphone

If you can’t remember your passcode, you'll need to erase your iPhone, which deletes your data and settings, including the passcode. If you backed up your iPhone, you can restore your data and settings after restoring your iPhone.

If you forgot the passcode on your iPhone:

https://support.apple.com/en-us/HT204306

You don't. You will have to erase your phone. Anything you haven't backed up will be gone.

See here: https://support.apple.com/en-us/HT204306

~Lyssa