[Solved] How to delete a Product

Maybe you should first read the documentation of using CosmosDB:
here

On this page you can see how you can query your product and then delete this record from your collection:

 var query = client.CreateDocumentQuery<YourDocumentModel>(UriFactory.CreateDocumentCollectionUri(databaseName, collectionName),
 "<your sql>",
 queryOptions);

with this result you can update the object (yourDocumentModelObject) and remove the product from the subcategory.
Afterwards save it back to the collection in doing something like:

await client.UpsertDocumentAsync<YourDocumentModel>(UriFactory.CreateDocumentCollectionUri(databaseName, collectionName),
yourDocumentModelObject);