When upgrading from Legacy Collaborate using OneDrive to New Collaborate your existing links to OneDrive will still function temporarily. Once you have configured New Collaborate, you will need to re-share your documents with your clients. This will re-upload the files to your new Collaborate Site and send new links to your clients to use.
There is no automatic process to transfer your documents from OneDrive to New Collaborate on SharePoint. You will need to remove and re-add your clients from the Sharing Settings, and manually re-share documents.
Once you have connected New Collaborate:
The Upload folder will no longer work on OneDrive. By re-adding your clients to the Sharing Settings, your clients will be sent links to the new Upload folder.
You will need to re-share documents to upload files to the New Collaborate site. This will ensure the client can access everything they need in one location - your New Collaborate site.