I forgot my iPads password how can I unlock it without having to erase all?

Sorry, there is no way to unlock without erasing if you have forgotten the Lock Screen passcode. 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 option is not available, you will need to use a computer. See: If you forgot your iPad passcode - Apple Support