Adding data during the registering process

Hi
Here is my issue.
I use the wix member registering form / process.
However, for each member, I need to have more specific fields. Thus I have my own “member” collection beside the wix one, in which we cannot add fields.
I need thus to synchronize the two collection, or at least when a member registers, elements are added on my own member collection with at leat id member and email.
Thus during the registering process, when approved, I need to feed my collection with nex user data automatically.
I don’t find where I can insert a velo code at this moment.
Thanks in advance,