Here’s how I do it:
1. Remove generic tape.
2. Fit Stans tape.
3. Put tyre on with inner tube, pump to ~40psi and leave overnight.
4. Let inner tube down, unseat only one tyre bead and remove tube.
5. Fit tubeless valve, try pumping tyre up.
6a. If tyre pumps up and bead seats, then let air out of valve, inject sealant through valve, and pump tyre back up.
6b. If tyre doesn’t pump up and seat, then add some sealant around bead and try again. Then 6a if successful.
6c. If tyre still doesn’t seat then use a CO2 cartridge. Then 6a.
7. Once tyre is up, if it deflates within a few days, repeat step 6a.
If none of that works, use a different tyre!
NB: Do not try this with cold tyres in a cold garage, as that makes them much less likely to seal. Simply using a hair dryer on a tyre for 5 minutes has turned it from impossible to seat to working easily on the next attempt!