The Data Filter widget has an output of type QUERY, which you can use as an input to your Service. You'll need to modify your +Service +to use this input. There is an InfoTableFunction called +Query() +(available from the "Snippets" tab), which takes an info table and query as a parameter. This will allow you to filter your info table.
Keep in mind, you'll need to bind data into the Data Filter widget for it to know which fields it can use to construct your query.