It is important that you start preparing for migration now; leaving it until the last minute will put your certification at risk. Completing a gap assessment will tell what you need to prioritize.
Then you need to ensure that you have had the right training. Finally, you have to show that you have implemented ISO 45001 for at least 3 months before your migration audit and completed internal audits and a management review.
You'll also need time after the migration audit to implement any corrective actions before a recommendation for certification can be given. Remember to consider festive holidays and that winter is peak audit season, so securing audit dates at the last minute may not be possible.