Seems like ProConnect does not support efiling a Superseding 1120S. So you might be better off just amend, and efile. See link:
Or Print and Mail it.
The idea is to avoid having to mail it. Never been a better time to avoid that in my opinion. There is software that offers a Superseding Return button and the IRS references the ability to do this as well. Seems like a fairly easy option to include as part of ProConnect. Not a lot of demand for it I'm sure but I would still expect to see it.
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