How do I delete an option group (civicrm_option_group)
If it's safe (AFAIK if the option group isn't part of an extension or the core, doesn't contain any option values, isn't used by any custom fields) you can delete it using the API explorer or a drush command.

On the 'Option Groups' screen, each group has a link to its page of options, of the form https://www.example.org/civicrm/admin/optionValue?gid=94&amp;reset=1 where the group ID is 94.

While logged in with privileges to the webserver directory, in sites/default, do:

drush cvapi OptionGroup.delete id=XX


Or go to civicrm/api/explorer, choose OptionGroup / delete, and add &amp;id=XX (where XX is the group ID) to the end of what looks like a URL string below those options, and click Go.