Could you please let us know the version of Lightroom mobile and which mobile device you are using?
If you are using an iPad, The first option (Marked red in the screenshot below), is of the filmstrip and can be moved from left to right using a swipe gesture.
Let us know if that helps.
I am using the the latest version of Lightroom mobile on my iPad, Version 2.7.4. I found my mistake was that I was using the iPhone LR Mobile app on my iPad which accounted for the problem.