BT_changed_transmission_lines.ino code consist of a library SoftwareSerial.
This Library allows you to select your own Tx and Rx pins.
For eg: In code, pins (3,2) is taken which means pin 3 of MCU is connected with Rx of BT and pin 2 to Tx of BT.
The default Tx,Rx pins can be used for other purposes.
Multiple serial port can be defined using this library
Syntax : SoftwareSerial mySerial(receivePin, transmitPin)