You can manage your tags in Guru in two ways: first, you can simply remove tags from a particular Card or multiple Cards. Second, you can permanently delete those tags so they will not appear on any existing Cards or appear as an option going forward when tagging future Cards.
Remove tags from a single Guru Card:
Navigate to the Card you want to remove the tag from.
Click on the pencil icon next to the tags in the bottom left corner of the Card.
You can delete any tag from that Card by clicking on the x icon next to the tag.
Remove tags from Cards in bulk (using Card Manager):
Navigate to the Card Manager.
Filter for and select the Cards that you want to remove tags for.
Click on the "Tag" icon and select which tag(s) you want to remove from the selected Cards:
Permanently delete tags:
This will permanently remove the tag(s) from all Cards it is added to and also remove that tag from the list of "existing tags" when adding tags to Cards in the future.
Navigate to the Tag Management tab under Team Settings.
Click on the tag you want to delete.
Click on Delete. You will see a note indicating how many Cards this deletion will impact.