This is a working solution to program MCP4728 DAC i2c address. It was tested with an Arduino Nano and a Teensy 3.2 but should work with other boards. Just change pins accordingly.
For bit banging the new addesss SoftI2cMaster library from https://github.com/TrippyLighting/SoftI2cMaster is needed.
Wire up SDA, SCL, LDAC, VDD and ground pin of the DAC to your development board. A pull-up resistor might be needed for SDA and SCL.
You can verify the success of programming with i2c_scanner from https://playground.arduino.cc/Main/I2cScanner
http://ww1.microchip.com/downloads/en/DeviceDoc/22187E.pdf