Hi there Henry and welcome
You will have to reset the phone, this will remove all the data from the phone and return it to new. This you cannot avoid sorry as it is the whole reason for the security.
To do the reset
Once done, you can then set up the phone again like when you first received it to be used.
If you have any problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the screen then submit, that would be greatly appreciated.