watch shows my max hr is 177. Try as I might, can only get it to 160. How to I get my watch to recalculate

You can enter the max hr manually, if you have a better value.

Oh yes, I know I can do that.  Just wondering if there is a way to encourage my watch to calculate a more reasonable max hr.  Am wondering if I should set my percieved effort at max when I do acheive max hr to let it know that was my max effort

I had a similar problem when I first got my watch. What worked for me was to enter my max hr manually and leave it for a couple of weeks.
When I did that, my VO2Max started dropping. This makes sense - doing the same activities, with the same average HR, was now at a much higher % of HRmax. During this stage, if I tried to re-enable HRmax auto adjustment, it would immidiately go back up.

However, once my VO2Max estimate stabilized, I was able to re-enable HRmax auto calculation and it's been stable ever since (so for about 2 years now).