Drop D is typically not something that would require a setup or any major changes, it’s just a bitch with a floating bridge, and typically you want to keep a Floyd guitar in one tuning unless you modify the bridge (we can get into that later if you like). For now, unlock the locking screws at the nut (usually 3 allen screws holding three little plates over the six strings.
then lower the low E string to D (down one whole step). From there, you will need to retune every string, probably several times, then lock the screws again, and fine tune at least twice more – just like when you restring.
Bam. Drop D. Chug away.