So you want to do

// M500 - stores parameters in EEPROM
// M501 - reads parameters from EEPROM (if you need reset them after you changed them temporarily).
// M502 - reverts to the default "factory settings". You still need to store them in EEPROM afterwards if you want to.
//define this to enable EEPROM support
#define EEPROM_SETTINGS

You will need to enable the Above line in you firmware