Here are some more suggestions for yellowing avocado leaves.
Since avocados are considered a plant that is generally free of diseases, TheGardenLady offers this list of possible problems an avocado tree can have.
Generally avocado trees are tolerant of a lot of water if there is EXCELLENT drainage. Drainage is very important. But if you feel that you have over-watered your plant, it cannot hurt to cut back on the water. Test the soil with your finger before watering again and water only if the top of the soil feels dry. The frequency of irrigation depends on the temperature. In hot, dry weather, the avocado tree may require irrigation every day.  As a general rule, a potted plant in a container measuring 6 inches in diameter needs water when the top 2 inches of soil feels dry to the touch. A larger container measuring 8 to 10 inches in diameter is ready for water when the top ½ to 1 inch of soil feels dry. Avocado trees like the soil to drain quickly.
Hopefully, when you transplant the avocado tree, you do it carefully because the trees have weak root systems and sections of the root balls can break off during transplanting.  See here.
Avocado trees prefer full sun but need protection from strong sun until they develop a deep root structure and dense foliage to protect the sensitive bark. So young avocado trees have to be slowly introduced to the sun or their leaves can yellow. See here. Even after transplanting them into their final planting site, if they have not become used to the bright sunlight, you might have to give them some shade at first.
To learn how to grow avocados at home or a container, you should watch this:
If you’re interested in why people fail at growing avocados, you should watch this:
If you’re interested in some helpful tips for the backyard grower, read this: