You can follow these directions in the link below to Repair a Corrupt Central Model (File-Based Worksharing Only).

https://knowledge.autodesk.com/support/revit-products/learn-explore/caas/CloudHelp/cloudhelp/2018/ENU/Revit-Troubleshooting/files/GUID-2DF59A60-A798-4528-8938-099D4E8E0D2A-htm.html