I have already completed the 1099 electronic filing and have a corrected 1099. 
I've changed the Box from 7 to 3 but how do I mark it Corrected and
how do I print just this one 1099?

1. In the 1099 Maintenance, on the single Payee form where you enter the 1099 data, there is a Corrected check box.  Check the box....
2. Click Print Forms and select the form you want to print.
3. On the Format Selection window (this is where you select whether the form is pre-printed and brand info) there is a checkbox in the lower left hand corner to select Corrected forms only.....