Go to the menu Sows/Boars and choose Animal- Entered Animals or Aniaml - PigVision - Breeding stock.
Use the green filter line to find the animal you wish to re-number as shown below with 306:
Click on the cell that shows 306 in white above (shown by the red arrow) and type the new number over the top of the existing one as shown below. I have typed in 306a and tapped Enter on my keyboard.
PigVision will ask you to confirm the number change from 306 to 306a. Click Yes to confirm the change or No to cancel it.
Once confirmed the animal's ID will now be changed to the chosen one.
If the sow is connected to a nucleus breeding herd in PigVision, the change will automatically be logged to the breeding company according to their validations.