How to add more than one tag or label to a contact on Facebook Messenger?

Here are the steps on how to add more than one tag or label to a contact on Facebook Messenger.

1. Click on the purple + sign at the left side of Messenger. 

A popup will come up.

2. Select the tags you want to assign to this contact like I have done below
and then close the popup by clicking on the X sign.

3. Wait for a few seconds, you will see that the contact will have multiple tags on Messenger.

Which you will see from the right hand side of the Messenger page: