How can I configure the Round Robin assignment between groups?

First, you must create a master group that is made of multiple groups. The master group’s members are considered for the Round Robin assignment in the form of a loop. 

Let us consider this example and understand how to configure Round Robin assignment between two groups, to keep it simple. You can follow the same process for multiple groups as well.
Follow these steps to configure Round Robin assignment between two groups:

1. Create a group, say Group 1, with A, B, and C as members. 
2. Create another group, say, Group 2 with D, E, and F as members. 
3. Finally, create a group called the Master Group with Group 1 and Group 2 as members.
4. Go to Assignment Rules and add the Master Group. You will notice that the members of both Group 1 and Group 2 are visible in the Members list of the Master Group.
5. Select Round Robin assignment mode.

Whenever records are assigned to the Master Group, they are assigned to the members of both Group 1 and Group 2 in the round robin fashion.

When a group member (user) is modified or deleted, they are removed from the Round Robin assignment.

To know more about Groups, click here.
To know more about Assignment Rules, click here.