Something like this:
char message[10];
int seconds = 9;
int minutes = 20;
snprintf(message, sizeof message, "%2d:%02d", minutes, seconds); // builds "20:09"
then message is your string you can print.
here is the doc on that function:
https://www.cplusplus.com/reference/cstdio/snprintf/
you'll find the specifiers (how you tell the format expected for the string) in the printf() documentation