The QGC IS NOT GETTING CONNECTED TO THE SIYI MK 15 and not detecting the serial port

I am trying to connect QGC inbuilt app on the mk 15 trx with the mk air unit but its not working

I changed SERIAL1_baud to 56700
I tried changing the SERIAL1_PROTOCOL to 1
Did same for serial 2 also
On siyi tx app selected connection is UART,under flight controller chooses PIX
baud rate to 56700
Then noticed that in QGC there is no comn link
Then tried create a comn link with the above baudrate and seleted UART. But then it throughs an error “ error on link Telem. Error connecting: could not create port. Unknown error” not exactly getting what to do can any one plss guide me.
Please refer to the image in the link

I am using Q ground control daily version “4.2.3.3 32” bit