Don't know how I can unlock the guide with PGTK. I have a LEX_PKG folder. Is it GPI file or IMG file?

I have created the file D046800.unl with Windows Notepad. I don't know what content I can put in this file and what format? I have a Garmin Nuvi 1490T with Unit ID:removed. Can I put "Unit ID removed, FID 900, PID 2, Region 0, VendorID 0" on the first line in the file D046800.unl? (Doesn't work anyway)
Do I need a KEYGEN program? Where can I download? Thanks!