In the case that I am not present at your ceremony to do the legal requirements, you will have to communicate that these have been completed (or will be completed). You can say something such as:

Letting everyone know that I’m not a legal celebrant. All of the legal obligations for <insert name of couple> have been taken care of prior to this ceremony.

If I’m present at your ceremony, you can say something such as:

Letting everyone know that I’m not a legal celebrant. All of the legal obligation for <insert name of couple> will be taken care an actual celebrant who is at today’s ceremony.