How to modify a tax return already filed
In the event of an error in the declaration, there are several possibilities depending on the type of error:
If you have deposited more or have declared a lower amount to be returned for Corporate Tax (a favorable situation for the taxpayer) , you can request rectification of the self-assessment presented before four years have passed since the deadline for submitting the aforementioned self-assessment ended.
If you have paid less or have declared a greater amount to be returned for Corporate Tax (unfavorable situation for the taxpayer) , you must present a complementary self-assessment , checking the "complementary self-assessment" box on form 200, indicate the receipt number of the previous self-assessment and fill in the "To be deducted (exclusively in case of complementary declaration)" box with the amount of the result of the previous self-assessment.
If the error refers to an information box or the account number in which the refund is requested, or another error that does not affect the result of the settlement , you must submit a request for rectification of the self-assessment before four years have passed since the deadline for submitting the aforementioned self-assessment expired.