Good question. No it's not through AMCAS, it's through AACOMAS. Below is the link.
https://aacomas.aacom.org/
Read the "before applying" and it will have the details on how to fill it out. It is a bit different than the AMCAS so it helps to read the Before applying portion.
It seems like you don't know too much about osteopathic medicine. Maybe you should do some research on it and shadow a DO first. In this way, if you do end up getting in and getting rejected from MD schools, you won't end up turning down the DO to reapply MD again like some unfortunate people do.