The easiest way is to use the Oceanlog software if you have it. If not. . .
You have to access the "SET U" menu. From the main screen press and hold the right button and side button (light) simultaneously for at least 2 seconds this will bring up the "SET F" screen DO NOT RELEASE the buttons. Continue to hold the 2 buttons as it scrolls through the SET F --> SET A and then SET U. Release the buttons. Press the right face button to scroll through the menu options until you reach TMT 1. If it reads OFF, press the side button to turn it ON. Then press the right face button. This will get the first digit on the bottom row blinking. Using the six-digit code printed on the transmitter (the first six digits that are together, not other digits that may be at the end) enter the first digit by using the side button to scroll. When you need to move onto the next digit press the right face button. When you're done with all six digits you can press and hold the left face button to save the code and return to the main screen, or you can press the right face button to move on to TMT 2.
Like MarineResearch said, the only way to test the link is to turn the transmitter on by hooking your 1st stage up to a tank and pressurizing it.