You have plenty of ilevel, so you’ll be fine. I know this might seem risky, but I’ve had a lot of luck with this. I simply say “hey guys, learning how to tank, bear with me.” I’ve been doing this since MoP and had great experiences. People offer help or they simply say I did fine.
The normal and heroic queues are pretty lax, and usually you’re grouped with some undergeared players so it was going to be a slow run anyways. People don’t usually get upset in those low stake dungeons.
What you will likely find is that tanking is way easier than you thought, but it will take a little time to move on to more difficult situations.
If you have some friends, ask them if they’d like to run some dungeons so you can practice tanking. This is surefire way of getting good feedback.
You’ll be fine. I’m a god awful player but I manage fine as a tank.