Just go to the program summary screen, hit the Program actions -> Salesforce campaign sync menu. Once in the dialog, revert it back to "none". This will not clean membership on both sides, though. You will have to remove members manually (in Marketo, this is done setting the program member status to not in program)
Then you can start the program-campaign sync process again.
Pay attention, it 's always preferable to create the SFDC campaigns from Marketo, in order to avoid any issue with program member statuses.