If you want to autosize a cooling tower, choose your tower You can replace the Performance Input MethodCoolingTower:TwoSpeed to be object for a UFactorTimesAreaAndDesignWaterFlowRateDistricCooling it can be auto-sized if you leave the default values.

As for the oversizing factor required by code, change object. Set your Sizing:Parameters Cooling Sizing Factor to 1.15.1.15. Run the simulation and search for the autosized value of the "DistrictCooling' and then replace the object with your CoolingTower and set the nominal capacity to be the same as the DistrictCooling.