Sync issues with Directory servers

Hello,

Some OU from SEPM are linked to our Active directory and we try to "Sync now", some OU's get this error message : The directory server from wich one or more organizational units have been imported does not exist. Ensure that the directory server exists, and then import the organizational units before trying to synchronize.

That we think is that OU have benn synced with a DC server that is offline now. It have a way to change the configuration of this particular OU ? Can we found what directory server is associated to this SEPM OU's ?

Thanks