How do I turn OFF do not disturb

You can do this in the Control Center. Pull the Control Center down from the top right corner. Find the Focus Button, just below Screen Rotate Lock and Screen Mirror, tap and deactivate the active profile.

If Do Not Disturb or another Focus profile activates automatically, then a Schedule is active. 

To disable or delete this schedule, go to:

Settings → Focus → Do Not Disturb → find SET A SCHEDULE → Tap into the time → tap Delete Schedule or just deactivate.

You can read more about how to use Focus here:

Use Focus on your iPhone or iPad - Apple Support

Read the above article. See the last three lines under “Turn on Do Not Disturb”. Use an almost identical process to turn it off.

Glad that helped. Enjoy your iPhone.