If we understood your query correctly then you want to increase one key with some value in a method call? If correct, then we have a way where you can share the document Id, key and the value that how much you want to increase. Our server will update that key value from the backend. And for this, I have recorded your request to provide the code snippet and new SDK which contain that API and it will be available in next release which is on 15th November. Once the SDK will go live, will update this thread as well.
Let me know if any other help required from our end. We are happy to help you!