How to switch schema in GraphQL Playgroud

I am new to GraphQL and try to test my GraphQL API in the Apollo GraphQL PlayGround.

This is what I wrote in server.js:

const app  = express();
const resolvers = {
    
    Query:{
        query1: func1,
        query2: func2,
    }

    Vendor{
        v_q1: func3,
        v_q2: func4,
    }

    Customer{
        c_q1: func5,
        c_q2: func6,
    }

}

const server = new ApolloServer({
    typeDefs,
    resolvers,
    ...
    }

server.applyMiddleware({app});

...

I read from this post that in the above example, Query, Vendor, Customer are called schema. While in my playground, I can only get access to the functions in Query Schema. I can search and found Vendor and Customer in the searching pad of "SCHEMA", which is on the right side of the page, while I cannot call the functions inside them, i.e. func3, func4, func5, func6.

I wonder how can I switch the schema in playground and call the functions in Vendor and Customer.