Already a Lead Auditor with many hours experience as a L/Auditor, Implementer and Trainer in both 9001, 14001 and OHSA 18001. I need to transition to ISO 45001 for Auditing, Implementation and Training. I participate in Advisera's Webinars from time to time.
While we at Advisera do not have an ISO45001 auditing or implementing course to offer, there are many available. I would suggest checking some of the main registrars in your area as they often provide training as well (for instance BSI, SGS and TUV). Remember that for internal auditing it is not necessary to take a certified course as the competence for auditor is determined by the company, and you can gain this competence in many different ways (including self study).
For a better understanding of the standard and how it transitions form OHSAS 18001, see this whitepaper: https://info.advisera.com/45001academy/free-download/twelve-step-transition-process-from-ohsas-18001-to-iso-45001