If you have MySQL already installed on your windows then go to services.msc file on your windows and right click the MySQL file and stop the service, now open your XAMPP and start MySQL. Now MySQL will start on the port 3306.
I had an issue with this because I had accidentally installed XAMPP to c:windowsprogram files (x86) which caused a Windows permissions issue.
The installation says not to install it there, but I thought it had said to install it there.
I uninstalled and reinstalled to c:xampp and it worked.