The output voltage is set with a resistor divider from the output node to the FB pin. TI recommends to use 1% tolerance or better divider resistors. Start by using Equation 3 to calculate VOUT.
To improve efficiency at very light loads, consider using larger value resistors because too high of resistance will be more susceptible to noise and voltage errors from the FB input current will be more noticeable. It is suggested to use a 10-kΩ resistor for R2 to start the design.