It is a little strange seeing a non payware aircraft that the default assignments do not work. Was this a payware aircraft at one time?
Now I have the ready for pushback B747-200 that was released as freeware that you have to go through specific tasks before you can start the engines and several other payware aircraft that have the same problem but realism is what you are paying for. I have a B737-800 NGX from PMDG and a CRJ 700/900 from Just flight that you can not use hardly any of the default assignments. The only one that seems to work is the shift E to open the main door
you have to go through the same steps as a real world pilot would on the real aircraft.