With Van Richten’s Guide to Ravenloft that came out earlier in the year it’s never been “easier” to create a horror adventure in D&D for this most commercial of occasions.
However you may want some further advice in a more concise format like say talking pictures.
A couple of days ago Kelsey of The Arcane Library posted a new YouTube video on how to write horror for D&D. Not only do we get some great advice but there is also a free adventure The Night Hunter for a party of level 1 adventurers to use this all hallows eve (or any other time) she wrote along with a walk through of running the adventure.
You can download the free adventure mentioned by Kelsey (and also linked on the YouTube video) here.
One year I’ll be organised enough to run a spooktacular scary one shot to participate in this yearly commercialized faux celebration. Until then “need more brains, uuuuurgh!”