All streaming options available for watching this movie are listed here - currently you can stream Spider-Man: Homecoming through FXNOW. This is a great streaming service with lots of good movies available. Spider-Man: Homecoming is not currently available to stream on Netflix, Prime Video or even Disney+. Even though it is a Marvel movie, Spider-Man: Homecoming is actually a Sony movie, so that's why it isn't available to stream on Disney+.
Currently you can buy/rent Spider-Man: Homecoming through iTunes, Amazon Prime Video, Google Play Movies, VUDU and Redbox. It will cost you as little as $2.99 to rent the movie and $13.99 to buy Spider-Man: Homecoming to watch online.