How to add Icon to button

Thanks, @domhnallohanlon.
But how can I use an icon on a button? An arrow to go back for example.

At the moment the way to do this would be by uploading an image to the button.

Here upload your image and set its resize mode to contain.

For simple symbols (like a back arrow) you could also always just use Unicode characters like this one:

There are libraries of free icons to download, like this one: https://icons8.com/

material.io is one as well

you cant set the icon size you want. trying to make smaller looks like icon is crop