The order was not correct, this is the right order:
Activate Wato Config on the slave site if this was disabled from the master
Disable Livestatus with omd config
Login to the slave site and create a new cmkadmin
Disable or delete the slave site on the master in the distributed monitoring section
Site should be useable standalone
Keep in mind that on the site are still all users and hosts from the main site which may be deleted manually then