I filed my 2018 taxes and found a mistake which means I owe additional taxes -- how do I do that on time?

[Leonard · Accepted solution]

You will have to file an amended tax return to correct the error your filed tax return.  The amended return Form 1040X has to be mailed to the IRS it cannot be e-filed.  You have 3 years to file "on time".  This link

 How to amend (change or correct) a return you already filed has information you may find useful.

[Edited 03/10/2020 | 9:53 am PDT]