Factory reset without Admin password

Hi all - I have 2 x T22P handsets that have previously been configured with another service provider and I do not have the admin password that is configured so I have no access to the device from either the web gui or handset.

I need to factory reset so that I can register to a different service provider.

I followed the instructions in the document "Recovery Mode on Yealink IP phones" and updated the firmware but it did not remove the existing configuration.

Is there any way I can return these handsets to factory default?

Appreciate any suggestions.

Cheers
Mal