Using Servo on Timer3 on a Leonardo
In file ServoTimers.hin standard Arduino Servo library change the timer

#elif defined(__AVR_ATmega32U4__)
#define _useTimer3
typedef enum { _timer3, _Nbr_16timers } timer16_Sequence_t;


on Windows the file ServoTimers.h is located in C:\Program Files (x86)\Arduino\libraries\Servo\src\avr