Your unit has to have received the Distinguished Unit with Merit Award the previous year. Meaning your unit should have had an inspection by your Regional Director, received "Exceeds Standards" on that inspection, and your unit should have a per-cadet average of (iirc) 20+ hours. This should have last school year (2018-2019).
In order to actually apply, you need to fill out USAFA Form O-761 and have it signed by your SASI and school principal. You then attach a copy of your unit decoration orders for the DUAM. Put all of it into a envelope and mail (yes, snail mail) it to Academy Nominations Office, HQ USAFA/RRS, 2304 Cadet Drive, Suite 2400, USAF Academy CO, 80840-5025.
Once you do all of this, then you technically have a nom (USAFA has to process it first though). However, only 20 seats can be charged to appointees from ALL JROTC and AFROTC units. You would be up against a lot of competition! Myself included, I just finished this particular nomination process.
Best of luck to you!
Edit: There are memos to your SASI and principal regarding what they have to do. Go to this site and look under AFJROTC:
https://admissions.usafa.edu/rrs/afrotc_hms_info.htm