Ok. I had done that already.
Does your health app show you your resting calories?
"Activity" gives a resting calories estimate. "Health" has a database for resting calories, also, but I have not seen Activity add data to Health for resting calories.
Frankly, unless you're being constantly monitored and eating a strictly controlled diet where all the variables are always known, it's better to just use this data to plan a rough idea of what you should be consuming/exerting per day. Filling out the green ring on the watch is a good way to do it, so is completing the red move ring. There are some online calculators to help find your base metabolic rate but even that is wonky. Depending on which one you chose, my BMR is 2,050, 1,800, or 1,660cals/day. I know my body fat percentage, so I chose the lowest number and try to eat less than 1,660 calories in a day, or make up for it with exercise.
But like I said, it's rough. Fretting over 10 or 20 calories here or there won't matter because online food databases aren't equivalent to whatever you put on your plate. You can get close, so use that closeness to identify trends and habits instead of minute data.