I have a button that shows for mobile and desktop users, currently its set as tel:123-456-7890. This works great for mobile users, but I want Desktop users to instead go to an anchor link #contact

I'll mention that I can't change the class name of the button but I can set an ID.

I'd like to change the default to #contact anchor tag, in case users don't have javascript set. Then if determined to be mobile, change URL to tel: else anchor tag.