Where do I put Settings button?
It really depends on your application, you could put them anywhere. However, considering most websites seem to have it in the top right corner, visitors may expect it there. I'd say left side wouldn't be bad - but putting it at the bottom is such a big change from the norm that you may confuse people trying to find it.
How do I add an icon button in Webflow?
Button basics. To add a button to your site: Go to Add panel > Elements > Basic. Drag a button element onto the Webflow canvas.