Enable developer console and press ` tilde (default button to bring up console)

After that, make sure to input the following commands:

asw_ignore_need_two_player_requirement 1

asw_skill_grenades_hornet_count_base [number]

asw_skill_health_base [number]

Replace number with a desired amount. I recommend setting health to 50000 and hornet count to 5000. This way you will be able to fly through the missions and ultimately get xp.

Note: If the cheats do not work, enter the console sv_cheats 1 code before entering these codes.

How to Enable The Developer Console?