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)]
Tab 'F 5 - Matings'
Select the relevant sow by choosing '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]
Tab 'F 5 - Matings'
Here you can enter the mating data by locating the relevant animal in the list.