What instructions were followed for the installation?
There isn't much to the install to have missed (Video)(pdf), and there is nothing to do on the printer itself, it should show immediately at boot, is it possible you left a piece of the tape over a sensor on the new tray?
Other wise the tray is defective (return it), or the correcter within the printer got disconnected internally, you would need some tools to get into it.
We have recently purchased a Xerox 550 Sheet Paper Tray for Xerox Phaser 7100 Printer,
Once this had been installed there is no option on either the printer server that uses this or on the web config in order to use the second tray.
The printer has been updated to the latest firmware and is only connected to via the Network.