Q:  How do I configure the TPS79601 to generate a 1.2V output voltage?

A:  Assuming R1 is the top feedback, R2 is the bottom feedback resistor and C1 is the feed-forward capacitor, with  R1 = 0 (i.e. short OUT to FB), R2 and C1 open, the output will be equal to the reference, which is 1.225V.  To go lower, you would need an external tight voltage higher than 1.225V and some extra resistors, as explained in http://www.ti.com/litv/pdf/slua256.  

If you need to go lower voltage at that power level, I suggest the TPS74x01 family.