How To Add A Tap To Call Button

Good Morning,
I am really enjoying the Swell theme. I am trying to add a tap to call button for mobile devices. I think I have the actual HTML coding pretty well in hand, so I think it will function properly, but I am at a loss as to how to make it appear on the mobile version. Where I would like it to appear is on the same horizontal line as the three vertical bars that denote the mobile menu.

See the site here.
https://www.chinatownmillbrook.com

Thanks for any you can offer.