Q.Geranium
What does it mean when leaves start to turn yellow?
There can be a few reasons for yellowing leaves, including watering issues, temperatures, pests and disease.
Here are some articles to help you pinpoint the cause and how to make adjustments.
https://www.gardeningknowhow.com/ornamental/flowers/geranium/geranium-yellow-leaves.htm
https://www.gardeningknowhow.com/ornamental/flowers/geranium/geranium-care.htm
Very likely it's from overwatering. This article may help you:
https://www.gardeningknowhow.com/ornamental/flowers/geranium/geranium-yellow-leaves.htm