yellowing of the lower leaves - burning on the leaf tips - upright at the leaf corners

I agree with NorCal_Kannabis. Leaves are the bottom/oldest ones. I'd just trim them off. If the whole plant is doing it then be concerned. I wouldn't go wild with the nutes trying to save a couple leaves either otherwise you're going to cause other issues. Your girls like healthy.

as you can see from your own picture.. those suckers are down so low and tucked so far back in that they get very little light.. in fact so little the plant has said die!!! she's self pruning nothing to be alarmed about. If you were to see this on new growth that is where issues like nutrient burns usually show first. deficiencies will show on leaves that aren't just shaded and i don't see any signs of that. I'd just pluck them off and let her grow.. she looks happy and healthy.. a bit droopy but maybe ya just watered.. also if that fan isn't oscillating i'd point it away from your plant at the side of the tent so it will still move and and create flow but not windburn your plants another sign of droopy leaves.. Happy growing! 👊

You are having a nitrogen deficiency. It starts at the lower branches and work it's way up. Your leaf edge curl up it due to heat stress and the tip turning brown is from nutrient burn. Check your pH and ec levels. Check your run off to check your ec to make sure your not locking out any nutrients.

It's natural for lower leaves to become yellow, wither and fall, as Nitrogen will go to the top of the plant where photosynthesis is being made. Adding more N now won't do anything on the lower leaves, they won't get greener, and you will burn your top leaves. Rest of the plant doesn't look like it's needing anything.