Are you able to read the temperature sensor? Are you able to convert the analog reading to a temperature?
If so, then turning an LED on when the temperature is between 20 and 25 degrees is simple:
if(tempC > 20.0 && tempC < 25.0)
At the same time i want to activate the servo when the light turn off and discativate the servo when the light is on
Doing this is more complicated. What kind of servo is it? If it is a normal servo with a 0 to 180 degree sweep, then you need to define what you mean by "activate it".
If it is a modified servo that has been turned into a continuous rotation servo, then it isn't a servo. You need to define how you want the servo to move when the temperature is below 20.0 or above 25.0.