Theres no way to do it without basic electrical supplies that you need to buy from the hardware or home depot store.

But if you do get to go there tomorrow morning, this is what I personally would do..

Buy the male 14-20 plug end, some 2 conductor wire (black or hot, white or neutral and green or ground, ground isnt counted in conductor count), and a female 5-15 or 5-20 receptacle, i would make sure the cable is an SOOW type or extension cord type and probably 12 or 14 AWG, no less not 16 AWG

Then i would go online and find what terminals are what on each plug end and connect them respectively, they should be;

White wire goes to each neutral or silver colored screw on 5-15R (or larger prong side) and neutral connection on the 14-20R

Black wire goes to the brass colored screw on the 5-15R, or the smaller prong side and to one of the phase connections on the 14-20R

Ground goes to each respective ground connection

Then go back online and double check you have everything right! Because electricity is no joke, especially that ground

Aside from this you would have to take the cover off and wire things directly to the generator wiring if you were in a true emergency situation, but that is kind of extreme