See the documentation at:
DTC3231 Library Documentation
Where there is the section on alarm bits and setting alarms:
// Alarm functions
void getA1Time(byte& A1Day, byte& A1Hour, byte& A1Minute, byte& A1Second, byte& AlarmBits, bool& A1Dy, bool& A1h12, bool& A1PM);
/* Retrieves everything you could want to know about alarm
* A1Dy true makes the alarm go on A1Day = Day of Week,
* A1Dy false makes the alarm go on A1Day = Date of month.
* byte AlarmBits sets the behavior of the alarms:
* Dy A1M4 A1M3 A1M2 A1M1 Rate
* X 1 1 1 1 Once per second
* X 1 1 1 0 Alarm when seconds match
* X 1 1 0 0 Alarm when min, sec match
* X 1 0 0 0 Alarm when hour, min, sec match
* 0 0 0 0 0 Alarm when date, h, m, s match
* 1 0 0 0 0 Alarm when DoW, h, m, s match
* Dy A2M4 A2M3 A2M2 Rate
* X 1 1 1 Once per minute (at seconds = 00)
* X 1 1 0 Alarm when minutes match
* X 1 0 0 Alarm when hours and minutes match
* 0 0 0 0 Alarm when date, hour, min match
* 1 0 0 0 Alarm when DoW, hour, min match
void getA2Time(byte& A2Day, byte& A2Hour, byte& A2Minute, byte& AlarmBits, bool& A2Dy, bool& A2h12, bool& A2PM);
// Same as getA1Time();, but A2 only goes on seconds == 00.
void setA1Time(byte A1Day, byte A1Hour, byte A1Minute, byte A1Second, byte AlarmBits, bool A1Dy, bool A1h12, bool A1PM);
// Set the details for Alarm 1
void setA2Time(byte A2Day, byte A2Hour, byte A2Minute, byte AlarmBits, bool A2Dy, bool A2h12, bool A2PM);
// Set the details for Alarm 2
void turnOnAlarm(byte Alarm);
// Enables alarm 1 or 2 and the external interrupt pin.
// If Alarm != 1, it assumes Alarm == 2.
void turnOffAlarm(byte Alarm);
// Disables alarm 1 or 2 (default is 2 if Alarm != 1);
// and leaves the interrupt pin alone.
bool checkAlarmEnabled(byte Alarm);
// Returns T/F to indicate whether the requested alarm is
// enabled. Defaults to 2 if Alarm != 1.
bool checkIfAlarm(byte Alarm);
// Checks whether the indicated alarm (1 or 2, 2 default);
// has been activated.
Based on your comment:
I checked that too. The example was too complicated.
You need to spend some time gaining a familiarity with some of the basic Arduino and AVR functions. To make this work you're going to not only need to understand how to talk to the RTC via I2C but also how to enable and respond to a pin interrupt in the AVR. You have the ISR function there but you have not done anything to enable any interrupt source.