how to apply pretension to a 32mm rod

1. i need to apply 3kN PRETENSION to a rod.
2. I already attempted:

"MEMBER PRESTRESS

2 TO 7  FORCE 3"

where to 2 to 7 are my rod members.

the error i get is "THE ABOVE LINE HAS ERRONEOUS DATA"

• Is there a specific format to input 'it'.?
• do i have to initialize load cases.?