Bike Hacks: Stubborn Tubeless Setup
There are plenty of reasons seating a tubeless tire can get tricky. Sometimes the tire is too stiff or too flimsy. Sometimes the shape of the rim keeps the tire bead from easily popping into its seat. But as long as there are no defects in the rim or tire, all that's really happening is the air isn't getting into the valve as quickly as it's escaping from underneath the tire.
The simplest way to fix that is to remove the valve core. Less obstruction means more speed and more volume. You'll probably have to let the tire deflate before threading the valve core back in, but the tire will be seated and you'll just need to re-inflate. And if that doesn't work, there's a way to get at least one tire bead seated all the way around so you'll get half the leakage when you go to inflate.
Remove the valve from the rim and pour out any sealant that may be in the tire. Then install an inner tube and inflate it until the tire is entirely seated. Deflate the tube, and carefully un-seat one bead entirely off the rim and remove the tube, being careful not to pull the other bead from its seat. Re-install the valve, pour in your sealant, and when you go to inflate it, you'll get half the leakage because the tire is already half seated. Thread the valve core back into the valve, and you'll be good to go.