TDEE recalculation?

Hey all - I need some advice / help please.

I have lost 37lbs in 14 months through cico. My exercise routine thus far has literally just been walking the dogs (aiming for 10k steps per day). With ocassional light weight training.

Today I took the plunge and joined a gym. I plan to go 3/4 days per week, whilst maintaining my walking.

I'm 34f 5'7 and 177lbs, with a goal weight os 159lbs. Currently eating in a 500 calorie deficit, so I'm eating 1370 calories per day.

My question is, if I'm going to start the gym, should I be recalculating my TDEE? (I assume yes). And if so, when do I start? I don't want to be over eating, but I'm also aware of the need to fuel my body for this increased activity.

Any help much appreciated!