First hit the drop down tag on this post to see I have 6
Go into your post and hit Edit
Scroll down to the bottom bar where your 5 tags are listed
Delete the very first tag ONLY, which is also the main tag for the post
Re-enter your new tag
Update the post and click the drop down menu to see you now have 6 tags
Up-vote this post so developers see ; )
or consider reading this and give me a likey : )
https://steemit.com/travel/@timelord/that-night-i-ended-up-lost-in-mexico-with-a-van-full-of-hookers