Rasmus,
You should be able to go into Host Onboarding (under Provision > Fabric > <fabric site> in DNA Center), select the switch in question, click "select al" to select all the interfaces on that switch and then click "clear" to clear any config on them. This is with 1.3.3.x DNA Center, so it might be slightly different on earlier versions.
Cheers,
Scott Hodgdon
Senior Technical Marketing Engineer
Enterprise Networking Group