You can set rules on your forecast since the what-if analysis is currently unavailable in QuickBooks Online (QBO), Marsha.
There are features in forecasting that allow you to set an increase or decrease in the amounts of accounts depending on the anticipated scenario, whether positive or negative.
Here's how:
Go to Reports, then hover your mouse over Financial planning, then select Forecasts.
Select Create forecast.
Set up your forecast, then Set rules to adjust values by a specific percentage, and then select Next to continue.
On the Forecast_PL, you can edit the Rules on the Forecast settings.