You need to log on to the web for that. So when you open the website you get the option to upload your video or when you're writing your travelogue and you press enter you see a + sign, that's another option for uploading photos and videos.
You cannt upload video directly on tripoto Create a channel on youtube(simply by clicking option on youtube) then upload the video on youtube.
After that copy the link and paste it on tripoto.
And also i think there is no option for video post on mobile app..You have to open the tripoto on laptop and then you will see a option of upload video.