How do I care for my yellowing corn plant?

Here's an article that might help you - https://www.gardeningknowhow.com/edible/vegetables/corn/yellowing-corn-leaves.htm

Place corn plants in a location that receives bright but indirect sunlight, such as near a south-facing window. Direct sunlight can scorch and damage the foliage. The plant tolerates low light better than direct sun, so err on the side of caution when selecting a location, although poor foliage growth will indicate the plant requires more light. Corn plants can't tolerate cold temperatures and grow best when the indoor temperatures remains between 60 and 70 degrees Fahrenheit.

Allow the soil surface to dry before watering, but avoid allowing it to dry to more than a 1 inch depth. Watering the plant until the excess begins to drip out the bottom of the pot ensures the soil is evenly moistened throughout. Use lukewarm water because cold water can shock the roots. Corn plants require less frequent watering in winter when they are semi dormant. A monthly feeding with a soluble fertilizer formulated for tropical houseplants, applied at the recommended rate on the package, provides sufficient nutrition. Apply fertilizers spring through fall. The plants don't require feeding in winter.

Great posts from chaz and Mogie, just like Freshcutky, I am marveling over a corn plant at that age. Never knew it was possible to have an annual last that long.

Maybe too much light? Maybe change the soil with new fresh dirt.