Help

Hi! I need assistance, please. I belong to a group of 15 people and we often come together to contribute funds for investment purposes. We started this in 2020 but I'm now facing a huge challenge as I no longer know how to calculate the interest due to each person because we keep adding capital and interest earned to the initial capital we started with. I'll be glad if anyone can recommend an Excel course I can take to fix the challenge. Looking forward to your response, thank you.