About encodeDownlink

I have a lora watch now, and every time I turn it on, it sends a data ‘/wD/’ synchronization time command, which translates to hex, which is FF00FF, My question now is how to receive this instruction in chirptack and then issue the synchronization time instruction through encodeDownlink. I also want to know how encodeDownlink works and what parameter is represented by input.data . When does encodeDownlink run
(Note:After the device is turned on, it will automatically send a request time synchronization command. Need to reply to the synchronization time data frame after receiving the synchronization instruction to synchronize the device time)