on 1120S I put employee's salary in line 7 instead of line 8

[DanielV01]

You are supposed to be able to.  It is the IRS' preference.  (Technically, they require it to be e-filed if the original was e-filed).  However, that is dependent as much as anything on the software you are using.  TurboTax Business does not support e-filing of a superseding return.  If this is your case, you would need to print out the return and write "Superseding Return" across the top of the front page of your 1120-S.  Mail in the return (and attach an explanation of the changes), along with all attachments as if you were otherwise filing an original return.  There is no X (amended) form that corresponds with Form 1120-S.

[ffrdacct]

I thought for superseding returns, we don't need to attach an explanation of changes?

[DMarkM1]

You are correct.  According to this link an explanation is not required for the superseding return.