How do you edit multiple video clips on Instagram?

Hi, I have a question about Instagram video section which for the life of me can’t figure out.

I’ve seen people that are able to take multiple videos they’ve recorded on their phone and upload them on Instagram. For example they’ve recorded 3 videos. All which are recorded at different places and different times but they can take snippets of these 3 videos on Instagram and upload.

I’ve found instructions on this, here’s a screenprint of the instructions: http://i93.photobucket.com/albums/l64/deadsy__x/Screenshot2014-03-04015216.png

But I have an Android phone(HTC One) and I don’t see the option of the ‘add’ button when I’ve uploaded my first clip. I only get the blue arrow(the next arrow) but there are people who can add more clips when they’ve already added their first.

How can I do this?