You may have an icon for the ad blocker extension in the upper right section of your screen. Check and see if it is one of those icons. If it's there, you can disable the ad blocker just for YouTube without removing it entirely.

If you want to remove the ad blocker extension completely, click on the 3 vertical dots in the upper right corner of your screen, then click on "extensions" in the drop-down menu, then click on "manage extensions."