Separate the accounts.
Record who owns the domain, app hosting, model account, database and document storage. Management access can be different from account ownership. The agreement should say how that access is granted and removed.
Name what can be exported.
Code, source documents, stored records, configuration and an index are different things. Some indexes can be rebuilt from the originals; other data needs an explicit export. Formats, licences and any proprietary tools affect what the receiving provider can use.
Plan continuity.
Agree the notice, copying and verification steps, the cutover and a fallback. Check which background jobs or integrations need to change too. Keep the old arrangement available for the agreed period while the new service is checked.
Finish the supplier and access changes.
Model usage, storage and other provider charges may continue while accounts or resources remain active. Record who stops each service, removes management access and checks outstanding bills. Secrets used by the old setup may need replacing through an agreed process.
Agree removal and retained records.
Deletion should cover the applicable stores, indexes, logs and backups under the actual service and retention rules. We identify exceptions and timescales in writing. Do not assume that removing a document from a screen instantly removes every copy from every system.