Step 1 - Navigate Credit Memos
Step 2 - Within the "Credit Memos" section click on the Add button - Select a Vendor, Select status = Available, See attached image:
Step 3 - Click Accounts. Apply the reversing journals.
Step 4 - (Final Step) - you will need to open the CM/Vendor Credit again and select "Edit Credit Memo". Click the checkbox "Force Sync With ERP" then hit Submit. Now your CM should synchronize with your ERP.