I connected to the Access Point correctly by the SSID ‘mywifi-xxxx’. I accessed the management of the AP with the IP adress, because the URL doesn't function. I couldn't complete the initialization wizard because I get the error. So the AP didn't delete the mywifi-xxxx. It was still in initialisation mode. I had two of the Access Points. I had no Problems with the first one. Yesterday I tried to disconnect the first one by pulling the power cord. And now it's no problem to connect to the second one and get the second ADMIN-SSID.
Finally, it's not possible to get access to another access point when the first one is already running. I wanted to copy all the Settings from the first one but in my case für the 5 VLANs it was faster to set it up again. Case is solved.
Greetings from Germany Matthias Just