I've created example for you. I have to add an extra selector to affect the element you want to change.

You shouldn't put anything into `content`

If you are not familiar with editing templates, the way is -> changing CSS (but it's a kind of "dirty hack"). Something like this: .fas.fa-pen-sq...

Inspect image in browser DevTools. If it's just a plain png - you can replace image on your server: just upload your new image with old name.