Tap on 'Groups' on the bottom navigation bar.

And then click the chevron to enter the group you wish to move animals from.

Highlight the animals you wish to move by tapping on them (find them by using the search bar or scan then with a reader while in the group).

Once you have highlighted the animals you want to move, tap the floating 'Action Button >>' on the bottom right of the screen.

Then on the pop up screen tap 'Copy/Move To Group'.

Then select the group you want to move them to.

You can either 'Move' them, removing them from the group you are currently in and adding them to the other. Or 'Copy' them, which moves them into the other group and keeps them in the current group.

Tap on 'Groups' on the bottom navigation bar.

And then click the chevron to enter the group you wish to remove animals from.

Find the animals you wish to remove by using the search bar or scan then with a reader while in the group.

Swipe from right to left on the animal to reveal 'Remove from Group'.

Tap on 'Remove from Group' and the animal will be removed from that group.