How to I recalibrate my Apple Watch

See the "Make sure that you earn Move and Exercise credit" section in:

Get the most accurate measurements using your Apple Watch - Apple Support

You should also make sure your watch is calibrated:

Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support

However when on a treadmill, if you are holding onto a handrail the watch has no way to know how many steps you are taking.

I have heard that some people strap the watch to their ankle while on treadmill or riding a bike. I'm not sure if it will still monitor heart rate though. You will just have to try and see if it works for you.

You're welcome.