There are a number of travel companies in the area who will be quite happy to take you to Universal, it is best to google around and see what you can find. The private tour companies may well be much more flexible when it comes to timings however.
I did this in November 2019. I looked at a few options. The tour companies didn’t have schedule flexible enough for my Universal park touring (i. e. rope drop, leave at park closing). I ended up renting a car for the day. Picked the car up first thing in the morning and dropped it off whenever I got back that night. I don’t remember the car rental company but it was on Katella, only a few minute walk from DL. It was less than $30 to rent. Hope this helps!