It is most likely hidden. To bring the icon back follow these steps:
GOOGLE CHROME :
Step 1: Click on the puzzle icon at the right top corner.
Step 2: Click on the pin symbol next to AdGone to pin it to browser tool bar.
MICROSOFT EDGE :
Step 1: Click on the puzzle icon at the right top corner
Step 2: Click on icon "show in toolbar" next to AdGone Ad Blocker
If above steps are not resolving the issue, please try to reinstall AdGone Ad Blocker by following this link.