How to upload file using graphql-client?

How can I make a mutation call from a client and upload a file?
I can do it in the editor (screen)

But I cannot figure out how to make the same from a client

var request = new GraphQLRequest
            {
                Query = query,
                Variables = new { id = "id" },
            };

            var graphQLResponse = await _client.SendMutationAsync<dynamic>(request );

where should I put the byte[] from an image?