Solution
You can do this in two ways:
Option 1:
Go to [1. input-edit] - [1.1. Sows] - [1.1.5. Mating/farrowing/weaning data (individual)]
'F 6 - Farrowing/weaning' tab
Select the relevant sow by pressing 'F 3' and typing in the sow number
Option 2:
Go to [1. input-edit ] - [1.1. Sows] - [1.1.4. Mating/farrowing/weaning data]
'F 7 - Weaning' tab.
Here you can enter the farrowing data by locating the relevant animal in the list