Mould is picked up somewhere while you are making it.
It would have come from somewhere within the process, either not having sanitised equipment, or super clean hands or the bowl you store it in between batches.
Kombucha needs to be treated carefully and anything that comes in contact with it needs to be as sanitised as possible.
If you do have mould growing on your scoby, unfortunately, there is no way to fix this and you will need to discard your scoby and brew.