When you click on those 3 little dots at the top right
You then can go to the far left and click on the 3 lines next to the word " Settings"
That brings you to a drop down menu and is where you will find Extensions
When you click on Extensions you will be able to search for AdBlock - then add it. You can also remove extensions that you do not want from this spot.
Please contact HelpDesk if you need further assistance.