To add meters to an existing group:
  1. Click on the group that you want to add meters to.
  2. Click the "+Add meters to group" button. This button is to the right of the meter icons that already exist in the group. In the image below it it towards the middle/right of the dashboard.
  3. This will take you to the Add Meters modal.

  4. check the boxes next to the meters you want to add.
  5. Click "Save" when you are ready.