Canon Printer on wi-fi needs psk number/code

You don't state the specific model of the Canon printer so it is impossible to be sure what it is capable of with respect to the wireless. If it is older then it may only work with 2.4 GHz and not 5 GHz. With the T-Mobile home internet mobile application on your phone you should be able to do basic management with your phone. You may need to either add another SSID for 2.4 GHz only and give it a pass phrase and then be sure to provide authentication the Canon printer supports. That may work. If the printer has an Ethernet port on it you can just use that to connect it direct to the gateway. Using an Ethernet cable, if it is possible with that printer, is the easy, fast way. 

Some older printers just will not play with the 802.11ax network standard. It is supposed to be backward compatible but older devices with older drivers often do not work with some newer gear. I can only guess that it is older and only supports 2.4 GHz on maybe the 802.11b/g/n standard possibly so it is a little more challenge but still might work.