Our son is a cadet at a SMC. I don't know if this is how it works everywhere but this is how I believe it works at his school:
There really was no "application" process. The ROTC leadership submits all of the freshmen cadets (who did not come in with a High School Scholarship) to the ROTC HQ (Maxwell). I don't know exactly what is submitted in the package but I'm sure it is the fitness scores, GPA, and probably high school transcripts. This happens early in the year. Out son was advised that he had received an ICS in February of his freshman year. This past year, the 1st year cadets were awarded the ICS in April. The ICS is retro to the semester in which it was awarded, so you will receive a nice refund if your cadet receives an ICS.
The information about the ICS was removed from the AFROTC website a few years ago. I remember looking for it two years ago for a friend and it was gone.
One thing to add......this year, there were students in AFROTC who were awarded an ICS in April and then advised that they had not been selected for SFT in May. Most of that had to do with the new process of having to declare rated or non-rated as a part of the SFT selection process. It was really tough time for these cadets in particular, having been awarded a scholarship one month and then learning that their AFROTC career was over the next month.
Also, the "word on the street" is that there will be fewer HSSP's and more ICSP's going forward but that is just "rumble". Given the current state of things, I'm surprised they are giving any at all.
I would advise your son to email the one of the staff in his ROTC detachment and inquire as to the process for ICSP nomination and selection.