How I can manually tag a user?

Yes, you can. Adding tags will help you to send the broadcast messages and even on sorting users. You can add a tag to multiple users with entering the tag details individually.

Check this video below to know more: (Updating)

It can be also done through the following steps,

• Step 1: Select Menu on the top-left corner of the page
• Step 2: On the audience section, click bulk action options to perform this action
• Step 3: Select “Add Tag” on the drop-down menu to add the required tag to the multiple users.
• Step 4: Select “Remove Tag” on the drop-down menu to remove the required tag to the multiple users.