Once stress prompts leaf yellowing, the leaves usually will not or cannot turn green again, so even if what you are trying is working to correct the issue, the leaves already discolored will probably remain so until they age-out and fall off (or are trimmed off, but don't remove too many of any live leaves for now, as that will hamper the plant's recovery).

Plant identification is important for diagnostics and care recommendations. Is this a type of Dracaena? (Our best guess, based on its appearance.) If so, they want to get somewhat dry between waterings (soil should become dry to the touch at least 1 inch deep into the pot, more if the pot is large) so the roots don't stay too wet. Over-watering is more commonly the cause of houseplant decline than under-watering, though both can cause similar leaf symptoms.

Make sure the pot has at least one drain hole that isn't blocked by a drain plug, and that the saucer it sits on to collect drained water is emptied promptly after watering so the pot does not sit in the extra water. (In that situation, the water may seep back up into the potting mix and stress or suffocate roots by keeping them too wet for too long.) When the plant does need water, water it thoroughly to make sure the soil is re-moistened all the way through the pot, and the excess should freely drain out of the bottom hole(s).

If the plant is near a draft of warmer or cooler air (like near an air vent or drafty window), that temperature change could cause some leaf discoloration or shedding. Insufficient light can also slowly starve a plant, and can cause leaves to lose their green color as the plant cannibalizes some of the resources in older leaves to supply younger growth. (This can also happen if a plant is under-fertilized, but this time of year, houseplants generally need little to no extra nutrients, since growth is slowing down.) Dracaena prefer bright indirect light, which can be provided by putting the plant directly in front of a window that does not receive many hours of direct sun, or by putting it near a sunny window. A grow light can supplement daylight if window light is not enough. Usually, the ambient light of an office or home lamps is not enough over the long term.

Some indoor plants, including Dracaena, can be sensitive to water quality, in terms of municipal additives like fluoride. Symptoms tend to appear as brown/dried leaf tips, though that can also be caused by low humidity, under-watering, over-watering, and other stressors. If you suspect water quality is a problem, you can try using filtered water, though obtaining purer sources like distilled shouldn't be necessary. Don't use bottled water if it can be avoided, since they often contain minerals like sodium for taste (sodium can damage roots).

Miri