Existing Azure file sync

I presently possess an established Azure file sync setup that is currently mirroring 400GB of data. This data is sourced from a nested folder located on a Windows server drive.

Now, we have fresh requirements to mirror the entire drive. I'm curious about the available options. Do I need to recreate the endpoint file sync, or is there a method to maintain the data that has already been copied and augment it?

Our ultimate objective is to initially synchronize an on-premises file share, and subsequently, carry out a transition that designates the cloud file share as the endpoint for our users.

I hope this make sense, and someone with more experience can assist.

Many thanks!