Make sure you include who you are speaking to. Address it to your home church, or to a Pastor or Elder at your home church who is in charge of group Bible studies.
Make sure to include relevant details of what a "course" is. Many people have different ideas of what a "Bible course" is. Be sure to clarify that it is a group event, but each person does the work on their own. Also include where and how to sign up:
Be creative! Make the video engaging and keep it short. Under 2 minutes for sure. 1 minute would be a good target.
Be yourself. Don't try to sound like someone else. Talk the way you would talk if you were in person telling your church about this opportunity.
Make sure to set your post privacy to public, otherwise those from your home church may not be able to see it.