To deepen the discussion, you usually need to alternately limit and expand the topic. Think about which method you need in which situation. If necessary, ask the other participants to help with the deepening.
Aim to find a specified topic for the group to discuss in more depth. “We have now discussed topics A, B and C. Into which of these would you like to gain a deeper insight?”
Ask the participants in which kind of issues they would like to increase their understanding. “What are the issues each of you would like to understand better?”
Encourage the participants to bring up such viewpoints related to the topic that have not yet been presented. “Can anyone think of something that we have not discussed in connection with this topic, yet?”