Suport for MKSbase was added during the last year. So if you are using 1.0.2 or below you cant find it.
It's
---
/**
* MKS BASE 1.0 – Arduino Mega2560 with RAMPS v1.4 pin assignments
*/
#include "pins_RAMPS_13_EFB.h"
#undef HEATER_1_PIN
#define HEATER_1_PIN 7
---
If that does not work for you you have to define your own pins. [reprap.org]
It's
---
/**
* MKS BASE 1.0 – Arduino Mega2560 with RAMPS v1.4 pin assignments
*/
#include "pins_RAMPS_13_EFB.h"
#undef HEATER_1_PIN
#define HEATER_1_PIN 7
---
If that does not work for you you have to define your own pins. [reprap.org]