Solution
There are two ways to mark a sow as non-pregnant (open):
Option 1:
Go to 1.input/edit 1.Sows 5.Mating/farrowing/weaning data (individual)
Navigate to the specific animal
On the 'Matings' tab, change the 'Preg. test' column to 'No'
Select the green checkmark to save
Option 2:
Go to 1.input/edit 1.Sows 4.Mating/farrowing/weaning data
Go to the 'Pregnancy check' tab
Select the animal(s)
In the 'Preg. test' column, select the 'No' option
Select the green checkmark to save
If desired, you can also set a default pregnancy test.
One-time setup:
Go to [4.Miscellaneous] - [3.Settings] - [3.Farm]
'Sows' tab
Under the 'Matings' heading, the last line shows 'default pregnancy check'
Change this setting and select the green checkmark to save the change