The Disneyland hotel said in a statement,

“At this time, reservations are no longer available, but if you stay at a Disneyland Resort hotel between May 31 and June 23, 2019, you can receive a designated reservation to visit Star Wars: Galaxy’s Edge during your stay [one reservation per registered guest; valid theme park admission required.”

If you don’t want to stay at the Disneyland properties,  you’ll have to wait until June 23rd when you will no longer need to have a reservation.