@Luca_Lattarini
If the schema is profile enabled then the best option is to make it non-mandatory as @vikash4 suggested. Here are some rules to understand the breaking changes https://experienceleague.adobe.com/docs/experience-platform/xdm/schema/composition.html?lang=en#evol...
To perform the cleanup, you will need to delete the entire set of records by deleting the dataset batches and then cleaning up the schema. Reconstruct the schema, re-create the API endpoint (if any) or reconfigure the batch ingestion/data mapping, etc and then ingest the data.
Thanks,
Chetanya