Actuals are usually going to be locked down by period so an accidental submission would fail in most cases. If the latest period of Actuals is still open and the user submits you could try the following: reverse the entries through a new submission (if you have the original numbers) or clear and reload the Actuals from source.
Keep in mind the same users aren't typically going to be loading Actuals and doing Planning as these are Accounting vs FP&A functions. Security should also be leveraged to protect who can write to the scenarios.
If you have people with dual responsibilities for Actuals and Forecast, then you could look into ConditionalInput as a possibility.
