how to chang my ntp server ip address externally

like using serial read() fill array like

mycode is

// Time Server Port
#define NTP_PORT 123

// Time Server MAC address
byte mac = { // LM: Substitute fake MAC address associated with IP
//0xAA, 0xBB, 0xCC, 0xDD, 0xEE, 0xFF
0x02, 0xB6, 0x7E, 0x00, 0x00, 0x02 };

// NTP Server IP Address
IPAddress ip(192, 168, 1, 225); // LM: DHCP address assigned by Asus router. Change this
// as appropriate for the implementation context.

byte a,b,c,d;

IPAddress ip(a, b, c, d);

You say "externally"? Are you talking about changing your router's port forwarding settings?

pls write full code serial read using fill the a,b,c,d

byte a,b,c,d;

IPAddress ip(a, b, c, d);

pls help me anyone