I prefer to put the M587 SSID and Password command in a "SETNETWORK" macro which I write to the SD card using a PC, and then run the macro from PanelDue.
If it's the version 3.0 PanelDue board, then the only way I can think of is to flash it with the wrong size firmware (e.g. the 5" firmware), start it up (which will cause it to delete the touch calibration when it detects the screen size change), then flash it with the correct firmware.
Problem has been solved. The problem was me. I did not have 3 check boxes checked in Bossa 1.8 that needed to be checked. I went back and re-read the instructions on DC42's blog and fixed my error. My PanelDue is now updated.