From the introduction:
This solo adventure is intended to be played using the pre-generated characters included in the Rebels of the Drifting City adventure. Alternatively, you may use any 1st level character you have created yourself.
You begin with the information as found under the 1st level character section on the pre-generated character sheets and additionally, you have 2 potions of healing. You regain 2d4 + 2 Hit Points when you drink one of these potions as a bonus action.
The key to playing a solo adventure is to play fair. If the adventure indicates you must pass a certain threshold for success, make sure to follow it. It is easy to try to fudge things, but it is more fun to play it properly. Roll your dice fairly and track your stats appropriately. Have fun.