You can add a tag to an account or contact that is within a List. Please follow the below steps:
1. From the Navigation Panel under Lists on the left-hand side of your screen, select List Builder.
2. From within the List Builder window, click Run on the list that you want to work with. Note: if there is no list on the page, please review this article on how to create a custom list: Monarch - Lists Builders - Adding or Editing a List
3.Check the box or boxes next to the account or contact you would like to add an activity to. Then click the Mass Actions button and select Tag Selected Items.
By selecting the Tag Selected Items option, you will be presented with a new window and the ability to search for existing tags. In the Search field, please type the first two characters of the tag. A drop list, listing potential matches appears assuming that tag is used in at least one other item. If the list is too long, you can continue to type in the field to narrow the list.
NOTE: The Tag has to already be existing in Monarch. If it does not appear when you search click Monarch - Tagging Accounts and Contacts to add at least one Tag manually. Then come back to Mass Tagging to do the entire list
Keyword Search: List Builder, How to tags, How to do mass tags, mass tagging