Great question — answering as the UphillTech team:
You can use an audited (that certifies that no data is used for further training) provider, but you have to trust the auditor. Alternatively, you can filter out the PII and replace it with anonymized data if that is possible.
Full answer by joerg-de: https://ai.stackexchange.com/a/49040 (CC BY-SA 4.0).
Need it done for your business? UphillTech.