email stuck in outbox. I don’t want to delete, I want to send. How do I do that?

This morning I learned that my sent emails from yesterday are stuck in my outbox.  I tried to resend this morning with no luck.  I deleted all but the one I sent to myself which is still sitting in the outbox.  I don't want to delete this one. I want to send it to make sure everything is working properly. What do I need to do?  All answers that I see point to deleting the emails offline.