Make sure all updates to your operating system and MS Office have been installed.
As of August 11th 2020 the latest versions are:
Version 2007 (Build 13029.20344) is the retail PC release of Word,
Version 1808 (Build 10364.20059) is the volume licensed PC version
Version 16.40 (20081000) is for Mac.
Remove the RCM add-in and then re-add it from the Office Store.
PC users: If RCM does not completely update or load in the sidebar, there may be settings in Internet Explorer that need changing.
1. Open Internet Explorer and access the Tools menu and select Compatibility View settings
2. Remove any checkmarks found in the boxes and select Close
3. Close Internet Explorer and reopen MS Word
4. Select the RCM tab and select the RCM button to load the sidebar
Mac users: If RCM does not completely update or load in the sidebar, try clearing your browser cache in Safari.