The method you use depends on how you created the prediction.
Increase a Freestyle prediction
If you're using the freestyle prediction method:
Select the periods to update.
Open Quick actions.
Select Increase by percentage.
Enter the percentage increase.
Apply the change.
Increase a formula prediction
If you're using the formula prediction method, multiply the value by the required percentage.
Increase another prediction
You can also reference an existing prediction within a formula and apply a percentage increase.
EXAMPLE: @exampleprediction *1.1
Increases the referenced prediction by 10%.