How do you add a temporary backup after your new device is set up?

So I had went to the Apple Store and we were setting up my new iPad and we were trying to add my old iPad’s backup. We had to go somewhere so we asked if we could do it at home later, then the guy taking care of us did something on the iPad which signed us in, so the iPad was done, except for the temporary iCloud backup. The guy told us that all the photos on my old iPad we be there and that I would have to download the apps myself, but only 200 photos came which I have on my phone, the temporary backup is still there it’s just not being used and none of my old pictures converted, now I would like to know, how do you put your temporary backup on a device that is already signed in?