If you are adding a new character, use a pdf sheet from the PCs section of this site. You can use the rules here to get caught up: Leveling Up – Rules – AoN, and please make the character make sense for whatever is already happening in the current mission.
You should start at the level here: Crew’s Current XP unless Hugh says otherwise.
What IS it? — Cat, “Stasis Leak” Red Dwarf