You might be able to get something from Unifi, a very long shot but worth a call. The business owner may need to call them since they own the equipment.
If the owner is locked out of their system, they may have legal grounds to force this, but they are going to have to do the work on that since you are not the legal owner.
In the end, I expect you are going to have to set up all the devices and hopefully import the config . once you get them attached to your controller. Best case would be if they have a local controller and a password to get into it.