The standard I2C clocks available are 50KHz, 100KHz, 400KHz and 1000KHz. If you want a 500KHz clock, then go to PSoC Creator -> I2C component customiser and enable the option 'Clock from terminal'. This will allow you to use an externally configured clock for component operation. In the clocks tab under design wide resources, look for the name of your clock. The nominal frequency has to be taken into consideration.
Please refer to page 16 of this document - https://www.cypress.com/file/183616/download .