Pulse frequency modulation is not directly supported by the PWM peripherals in CY8C24894, PSoC1 family. It is also not directly supported in many MCU families.
The best approach to PFM with a PWM peripheral would be to load the period and the compare register on every change in the reference.
Kindly refer the 8-Bit Pulse Width Modulator Datasheet. On page 9, you can find the API function PWM8_WritePeriod . On page 10, you can find the PWM8_WritePulseWidth. By loading these two values in the PWM User Module, you can change the frequency, and maintain a constant duty cycle. If you want the on time to be constant, you can change the period alone. Depending on the range of frequency you want in your PFM output, you can choose PWM8 or PWM16 or PWM32.