Change current of bandgap
You have a feedback loop (the two branches n the left) and an output stage (the branch on the right).  The formula you show is for the feedback loop.  K controls the voltage drop across the resistor in the loop.
The output current can be changed by the PMOS current mirror ratio between the output and the loop branches. The resistor in the output branch will control the output voltage.  In order to get a temperature independent output voltage you need to bring the output resistor, output diode in harmony with the loop resistor and diodes.