It appears that I’m allergic to my watch what can I do

It could be a fungus infection. I would clean the watch and strap and then put it on the other arm until the reaction disappears and see what happens to the other arm.

Don't shower with the watch. You will always need to take it off afterwards to dry the skin under the watch and to dry the watch before putting it back on. Instead take it off before shower, clean it and dry it. Let it air dry until after your shower.

If the watch or arm gets wet then take the watch off and dry it.

I think Garmin also is interested in getting info about these reactions so contact them: https://support.garmin.com/

If it is a reaction to the strap one option could be to get another type of strap like one in leather or metal.

Clean the watch regularly (see the instructions in the document Wear and Care Tips for Garmin Watches), swap the wrist wearing it daily, or for the night.

Get a cover for the charging contacts like the one shown below. Some people are allergic to metals. I've got 10 of them for free from AliExpress when ordering a spare charging cable. 

You can also try disabling the PulseOx, or HR functions to see whether the irritation does not come from the photosensitivity that some people suffer.

If nothing helps contact the Support - see also the comment of seilogramp in this thread about it: Skin irritation under laser point

Which Garmin watch is this? Once I know this, I can move this thread to the the correct hardware forum.