To do either one of those business returns you would have had to use the Business Desktop program. So you should still have the Business program installed? You can't do them online. You probably have to amend the 1065 Partnership return to zero? And then do a brand new 1120 S return. You can't amend the 1065 to be a 1120.
Or do you mean when you signed up with the IRS to get your EIN?
Yes ... you need to amend the partnership form 1065 & file an 1120-S . If this was the first time filing a business return I highly recommend you seek local professional assistance to get this straightened out and to avoid penalties.
I concur with @Critter in that it is best you consult with a tax professional.
Really at this point, we don't have sufficient facts to provide clear guidance as there are a number of questions:
- How was the entity registered with your state of domicile
- When did you register the entity
- Did you make the appropriate election to be taxed as an S corp
- Did you receive confirmation from the IRS regarding your election to be taxed as an S corp
Depending on the responses, there could be additional questions. As a result, this forum is not really the best to go back and forth with questions and answers. This is where it is best to have a face to face with a tax professional and provide guidance.