you click the bubble on the bottom and freaking type

I think you might have the version that isn't updated, yet? Like my phone. What you do is click on the collages you want to comment/remix and you should be able to... (Sorry if it's not very helpful)

all you do is click the bubble that looks like the bubble on the messenger app the start to type💜💜💜💜💜💜💜 plus use lots of EMOJIES