Velvet preservation starts before you shoot! Need to have all the supplies etc ready to go if you want to save it. Also late in the season, if the velvet is starting to strip it's probably too late any way and not worth the effort and money anyway. As mentioned call the taxidermist asap and hope they have what it takes.
Throw it in the freezer as soon as possible and get it to the taxidermist. If its too late, and you HAVE to have it with the velvet, they can apply artificial velvet (flocking). Congrats to the young man!!
Haven't done deer, but for caribou I left it in "freezer" (outside, since we lived in AK) for the whole winter once I knew it'e be consistently below freezing.
4 months later, even with a few thaw days, all was good.
Get it in a freezer ASAP and bring it to a taxidermist. You can soak them in white gas and it preserves it. touch it a little as possible. If some of it got ripped be hard to save those spots.