The easiest way is to use the Helper link at the top of the Parmeter screen.
For the long version, read on:

To extend the due date for an individual student, do the following:

1. Select the problem you want to extend the due date for.
2. Click PPRM on the remote control.
3. At the Set Course Parameters screen, type the user name of the person 
you wish to extend the problem due date for.

Note: If you don't know the individuals user name, select the select user link. 
A new window will open with a list of all the students in the class. Select the 
student.

4. Click Update Section or Specific User.
5. The table that is displayed will have a heading labeled User_______ at domain________,
Under that heading will be a column labeled "For Resource", scroll down to the due date
cell and click on the link
6. A new window will open, enter new due date.
7. Select Store.