To change an input value during a dynamic simulation you'll need to run the simulation as normal up to the time where you'd like the value to change, change the value, and then resume running the simulation to the desired end time.
To vary the wind generator's power, you'll need to change the appropriate parameters for the dynamic model you're using which can be found in its documentation. You may need to consult a block diagram or datasheet to find the appropriate parameters.
You'll need to consider whether you want the power output for the whole site to change via the PPC, or whether the desired change is at the turbine level. You may also need to consider whether a control mode needs to be toggled to 'unlock' the turbine/PPC to follow a new active power command.