video won't allow edits if made from a presentation?

In order to add audio to my individual slides, I turned it into a video. Now, I'm seeing some timing issues within the same scenes and can't edit them. For example, scene two has a speech bubble containing some text, now it is apparent to me that the timing of the two are off, I can't figure out a way to edit it.

Video won't let me access the layers 

Thank you,

Deb