in soil , yellowing is almost always water issues , often because pots are too small
inconsistent water causes PH problems & in turn nutrient lockouts
the biggest problem though is loss &/or charge of biology , the little critters in the soil that feed & protect your plant will die , go dormant or POQ
the loss of chlorophyll in leaves will play havoc with photosynthesis causing plants to take forever to finish & the longer they take to finish without the soil biology in place to protect the plant the more susceptible to pest & pathogen attack
there is no quick fix for this although over watered pots can be left to dry out but with over watering you've already promoted the pathogenic organisms from the lack of air in the media so damage can already be done
for under watered pots in a peat based media the top soil can be hard & dry & usually pulls in from the side of the pot or shrinks because the peat has become hydrophobic making it hard for the media to except water
some ways people have attempted to fix under watering especially in fabric pots is to transplant the complete fabric pot into a bigger fabric pot with more of the same fresh soil , not always done because like you it's always late in the game & growers can't justify the expense
the other is to water really really slowly , the idea here is to put a very small amount of water on the dry soil surface which should pool & sit trying to re hydrate the peat , if you put too much water on the surface the weight of the water will just run through the pot to the bottom & re hydrate nothing along the way , once the surface water has disappeared leave it for 15 / 20 min then repeat
keep going until you get minimal runoff , keeping in mind if you put too much water on the surface it will run through the pot & show runoff , start by feeling the weight of the pot , it should feel lite if it's been under watered , what you want to feel is weight without runoff so you know the water is staying in the pot & re hydrating the media
yellow leaves will never recover back to green so what your looking at is the green leaves staying green to know your solving the problem but this late in the game you'll run out of leaves before the plant gets to finishing in most cases is my guess & you'll be forced to harvest early
shit happens mate we've all been there , just move on to the next grow