Adding existing outdoor cameras to my new Ring Alarm setup?

Hi, Hoping to get some guidance on this. I’m soon to move back into my house after remodeling. My contractor installed 3 Ring floodlight cameras at the house to protect during construction. He had access to these cameras on his own Ring account. He is giving me the cameras as a gift and leaving them there upon completion. I am ready to install my Ring Alarm system and would like to add the 3 cameras to my account (setup) so that I can monitor the video on my account and stop him from seeing the video on his account. How do I do this?