If your animals are already assigned to a group but you want to move them into a different group, there are two ways to do this.
From the Actions screen
When importing a session you will see an action appear on the actions screen informing you the animals have been updated in a group.
Click Assign to move all or some of the animals into a group.
You will be able to split the animals into different groups in the same way as you would when first assigning animals to a group.
From the Session Summary screen
If you no longer have an action for a session on the Actions screen, you can move animals into a different group when viewing them in the session.
On the Sessions screen locate the session that contains your animals, click on it to go to the Summary tab. From here click the Assign button next to each action to move some or all of those animals to a different group.
You will be able to split the animals into different groups in the same way as you would when first assigning animals to a group.
Choosing which session to move animals from
When you move animals from one group into another group, any weights will move into the new group from the session you choose and any sessions recorded after it.
If you make a mistake assigning an animal to a group and want ALL weights for an animal to move into the new group, you will need to find the first session that animal was recorded in and move the animal from there.