One of the changes that we made a couple of years ago specifically to support training new officers is that we enabled members that were designated as "Other Officer" in Membership Management to be assigned access rights for specific admin modules in FTH.
Thus, what you can do is to first make the new officer an "Other Officer" in Membership Management, then assign that person to have access to the same stuff as you in the Access Settings tab in Website Settings. You will still be subject to the 3 person max for access rights, but this does give you a way to assign new officers access rights for training purposes.
Additionally, by making the person an "Other Officer", they will be included in the officers email list, so if your club is using that list, they will also get those emails.
Relevant User Docs:
support.toastmastersclubs.org/doc/item/access-settings
support.toastmastersclubs.org/doc/item/m...-panel#officer-roles