Assuming the off-air module is plugged in, and the antenna is up, the locals should appear after the installer calls to activate your account. You may need to perform a reset (by holding the power button on the box for 8 seconds) after the call to activate programming. Then leave the box off for 10-15 minutes while it downloads all the guide data. If you try to watch TV while it's downloading the guide data, it may take 2-3x as long.
He should have plugged the OTA module into the back of the VOOM receiver.
He should have verified that the off-air antenna cable (after separated using diplexor) is plugged into the OTA module.
He should have called to activate service.
At this time, you may need to reboot the receiver by pressing and holding the power button on the receiver for 7 seconds.
Let the VOOM receiver sit for 12-15 minutes. Do not turn it on.
At this time, you should see local information in the guide. If you see your locals in the guide, but can't tune / watch them, the installer will need to repoint the off-air antenna. DTV/HDTV locals reception is sensitive to antenna orientation. If the provided antenna is inadequate, he will need to request a new / upgraded antenna.