If you’re asking how to get from LaGuarda to JFK, he best way to get to JFK from LGA is by taxi. A yellow taxi line outside all terminals at LGA is the fastest or you can call a private taxi service to pick you up. I shuttle between both airports a lot and I use Kew Garden Taxi. Just call them and they will pick you up in a matter of minutes for a flat fee.
Their phone number is (718) 846-5800.
Hope this helps.
If you’re asking if the International JFK Hotel, a hotel near JFK, offers shuttle town car service new york ny to LGA, you’ll really just need to call them and ask.