Red spot on wrist

Skin irritation like that is often caused by bacteria. Bacteria love the warm and humid atmosphere under your watch. Some advises:

• To get rid of the skin irritation, wear your watch on your other wrist for some days
• To prevent irritation, wash the back of your watch, the strap and your wrist every day (and after every activity) and dry everything before you put it on again. I for example take the watch off and clean it with warm water every time i take a shower. Also wear your watch a little more loosely (so that it still has room to move around by 1-2 cm) outside of activities. Only tighten it for activities where you need an accurate wrist heart rate reading. 

thanks. i do all that already. except the part of wearing it loosely. will try that. thanks

See How to Avoid Getting a Rash From Your Fitness Tracker for some general info from medical experts.