I have bump filled with blood on my salivary gland under the tongue not on the tongue what could it be, what to do?

See a dentist: Sounds like a blocked salivary duct or a stone blocking duct. Better safe than sorry. See a professional for assessment.

Can be alarming: The red bumps underneath your tongue have been caused by irritation most of the time. Should the bump get worse, or get painful or last longer than a couple of weeks, you should see your GP for exam.

Probably: A benign hemangioma but get check by a dentist/oral surgeon.