I thought this might be a good resource for Occasional teachers who are working on-the-go like me. It is a series of short YouTube videos from Homework Help:
An activity that you could do if you had a long block would be to have pairs of students select a video, and if it is silent (a screenshot of a session), have them narrate it to the class. One student can be the tutor, and the other can be the student.
If there is only one device in the room, the teacher can select students to narrate a video that they choose.
Then, students can evaluate what helped them, and what they are still a bit confused about.
Afterwards, the teacher can provide a tutorial for students who wish to sign up for the service.