It can be frustrating if you can't find the party you wish to post to on your list when scheduling your template! Here are some tips to try:
When looking for a group:
Try relinking your account to FB:
Click here to learn how to relink your account
Make sure your personal profile is an admin of the group. If you created the page on your business page it is possible that only your page is the admin and not your personal profile as well (if it's a Business Page Group and you are not an admin of the Business Page it would show up in your Personal Group list as long as your personal profile is an admin in the group).
Make sure the app is added to the group
Make sure you're checking correct list, the Personal Group list should show any groups created on your personal profile and the Business Page Group should show any group created on or linked to your Business Page.
Make sure it was created in a group - FB does not allow 3rd party programs to access Facebook Events.
When looking for a Business Page:
Make sure your personal profile is an admin in the page.
Try relinking your account to FB using the instructions above.
If you are still unable to find your party in the drop down list please reach out to support using the help chat button in the right hand corner of your account so we are able to assist you in locating it.