Ask a student (in advance or in the class) that wants feedback on their weekly reflection and distribute their reflection with the other students in the group.
Ask all the students to read the reflection and give (constructive) feedback based on the assignment in the course manual.
A good reflection is: Not opinion, but also not a summary. Talks about the materials in detail and relates it to own ideas. Contains an argumentation. Ends with a couple of questions that are interesting to discuss.
This should be done somewhere between week 2 and 4.