I stumbled on this handy tip here.
Sometimes passwords fail to get documented properly.
If that’s the case, you can reset the appropriate account password or create a new db_owner by running SQL Mgmt Studio as SYSTEM via PsExec.
Once you have PsExec run with options -s and -i with the path to you Ssms execuatable:
PsExec -s -i “C:\Program Files (x86)\Microsoft SQL Server\110\Tools\Binn\ManagementStudio\Ssms.exe”
Sql Mgmt Studio then launches, then click ‘Connect’ to login as NT AUTHORITY\SYSTEM.
JUSTIN | BLOG 