Hello ImaCircularSaw!
Do you have access and rights to the ConfigMgr admin console? If not, get the admin in your organization to browse Advertisements and make note of all OS Deployment advertisements.
For each OS Deployment Advertisement do the following: Right-click, Properties, General tab. In the General tab you will see the Collection that is targeted. Make note of each Collection per OS Deployment Advertisement.
After you have noted all of the targeted Collections, browse each Collection until you identify the server in question. This is the collection that the server needs to be removed from. Remove the server from this Collection.
Once the server is successfully removed from the Collection you may then trigger a "Machine Policy Retrieval & Evaluation Cycle." This can be done from the server's ConfigMgr client located in the Control Panel. Please do the following: Control Panel, Configuration Manager, Actions tab, highlight Machine Policy Retrieval & Evaluation Cycle and press Initiate Action. At this time the ConfigMgr client should recognize that the OS Advertisement is no longer targeting this server.
The server should now be free of the OS Advertisement.
/cheers
