How are you downloading the firmware to your device ? Are you downloading to the RAM or EEPROM. if you are downloading to the EEPROM, you need to RESET the device for it to renumerate. Either way, you need to download only once. What is the behaviour seen after you download the firmware for the first time ?
If you want to know how to refer example for assistance, please refer the ControlCentre exaple source which you can find at C:\Cypress\Cypress Suite USB 3.4.4\CyUSB.NET\examples\Control Center after you install SuiteUSB (http://www.cypress.com/?rID=34870). This example include both kinds of download (to RAM and EEPROM ).
it's Ok now. Sending a vendor request of A0 with wValue = 0xE600, wIndex = 0x0000 and data byte of 0x00.) it works well now