To add a new line 5. Get into Configuration by dialing "config" on your M7310 set, then your password. A template is needed to navigate your keys-Forward, back, heading and show. If you don't have it, it is the 4-square cap keys below the display. There are 2 on the left. The top on the left is the heading, below it is the back button. There are also 2 on the right. The top on the right is the show, below it is the next key.
After getting into programming, you will see terminals and sets. Go next to lines. Press show, your display will display line 001, press copy, look at your display, and copy line 001 to 005. Your line 5 is now programmed.
Then you have to allow your sets access to this line. I'm not sure if you are setup as a key system-"all lines appear on all sets" or as a hybrid " lines are in a line pool??
But you can add line 5 to one set, then copy the others. email me back if you need more help... Chris W