Nevermind. I got it. Not pretty, but the answer is to write a byte array to the DSD board. If you are using the BLE coding example from the b4x forum, then:
manager.WriteData("0000ffe0-0000-1000-8000-00805f9b34fb","0000ffe1-0000-1000-8000-00805f9b34fb", Array As Byte(0xA0, 0x01, 0x00, 0xA1)) 'Turns off DSD Relay #1
Also, a few points because we are dealing with BLE:
My T-Mobile Android 9 Samsung a10e phone had to do a T-Mobile software update and power-off reboot before the BLE sample program would connect with it to the DSD board via BLE.
Well, actually, it connected 1 time, then never again... until the upgrade and reboot.
Oh, and it wouldn't do BLE when the phone was below 30% charged.
Each of the above generated errors.