Tenant asks owner to do this work (presumably via the letting agent). If owner is supportive, owner applies for permission from the OC. Strata manager can help the OC out by gathering all necessary documents from the owner. This may include plumber licenses, warranties and insurances. Owner may also need a by-law. When the OC has given approval (after reviewing these documents), the owner can arrange the work – the role of the letting agent may be to arrange and manage the installation if that’s what the owner wants.
Note that I’m in NSW so some terms and practices may be different.