He "adjusts" the loop parameters by changing the gain, dominant pole frequency, or dominant zero frequency.
Fixing the ringing is not that intuitively obvious. In a standard type of pll, where there is an integrating op amp in the loopfilter, there input resistor R1 connected to the inverting input, and the op amp output is fed back to the inverting input via a series RC pair, R2 and C. Then the product R1 and C determine the pole frequency and "gain" (gain is a function offrequency). The product R2 and C determine the zero frequency. In a crude way, one can then vary the R2 value around to try to move the zero frequency closer but always above to the pole frequency, which gives more phase margin and less ringing.