You can change the icon of the scroll to top according to your choice with Zakra Pro Add-on.
Follow the steps below:
From your dashboard, go to Appearance > Customize > Footer > Scroll To Top.
Under Icon option, select any icon of your choice.
Click on Publish.
It is shown in the image below:

Follow the steps below:
From your dashboard, go to Appearance > Customize > Footer > Scroll To Top.
Under Icon option, select any icon of your choice.
Click on Publish.
It is shown in the image below:

Updated on: 15 / 10 / 2020