bluetooth audio receiver pair name change error by onboard serial

[arvindgr]

My 1st question. I've got a cheap PT-810 bluetooth audio receiver whose chip is very clearly pictured at https://www.eevblog.com/forum/beginners/bluetooth-module-noise-issue/

My aim is to rename the Bluetooth pair name, default is PT-810 to something else, since I use many such modules around me, After a lot of search I was guided by -- How to change Bluetooth music receiver's name and other settings using a serial converter (or otherwise) http://electronics.stackexchange.com/questions/191071/how-to-change-bluetooth-music-receivers-name-and-other-settings-using-a-serial --- and hence followed hobbyist site's bluetooth-module-configurations instructions from same post But since @QuestionerNo27 seems to have issue with USB-Serial converter, I had on-board serial port which had D-type connector, I felt positive. I connected RX-TX and TX-RX of Serial port no. 2 and 3 to soldered RX&TX pins of bluetooth. But after verified proper connections Result is just Square BOX!!! in serial moniter... Please guide me where I've went wrong while many like me are deperate to change this name...

[arvindgr]

Did you connect the GND pin? Did you set the correct baud rate?

Since the whole motherboard has common GND, USB and serial port's 5 pin is common GND and hence wasn't possible to externally connect them. Also, The site asked to mention less than 115200 bauds while I was much lower at 9600. Can you help me, with what Those square BOXES in output denote?..