How should i adjust my fitness routine if i'm switching to a more active job in 3 weeks?

Depends on your goal: If you need to adjust your routine to prepare for the increased activity of your new job, then focus on endurance exercises. This would include increasing reps and lessening the weights used.

Why adjust: For what reason would you be adjusting. You might need to make a schedule adjustment, but not knowing what you do or will be doing, i cannot begin to answer your question.