How do I print in a simplex (single page) mode?

[Just-Lisa-Now-]

Do you mean how do you turn off 2 sided (duplex) printing? 

or are you asking how to only print 1 page of the return at a time?

The term "simplex" has me confused.

[Just-Lisa-Now-]

2 sided printing is a Windows printer setting you need to turn it off in your Windows printer settings, ProSeries doesn't have any control options for this.