You can bulk update Tags from a list or Report in Prospect (note: this only works on record types that already support Tags e.g. Companies, Contacts, Opportunities, Documents etc.,). This is a much easier way to assign or remove Tags in bulk, rather than one by one.
You'll need CRM Bulk Update Rights to follow the steps in this article
Step 1: Navigate to Companies
In the navigation menu, click on 'People & Places' and select 'Companies' from the drop-down.
Step 2: Perform Bulk Action
In the further options menu (three dots in the top right-hand corner of the page), select 'Perform Bulk Action'. This gives you the option to either 'Select All' or individually select the Companies you'd like to update by ticking the tick box to the left of the Company name.
Once you've selected your chosen Companies, click the 'Choose Action' button towards the top of the screen.
You'll then see an option to 'Update Tags'.
You can then choose to either bulk remove or bulk update Tags in the next step.
Once you've added and removed the Tags that you wish to change, click 'Update' to confirm your selection and update the records.