how to handle synchronous databse query in node.js

Question

I am new to node.js, and I am starting with login and signUp implementation, and I have just found that my database Query of MySQL failed to execute in sequence. So what I do is to find does username match exisiting usernames in database, and invitation codes, if there exist, I will send my JSON file with property true, otherwise false, but I have just found, the json file is sent before the database query is finished, so that even if user name matched, the response property is still set to false. I tried async and sync but I still have trouble understanding and fixing my error, can someone please help me on fix or a better alternative implementation in this case? Thank you!!

Here is my code:

// build up connection to db
const con = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  password: 'pwd',
  database: 'test'
});

// async function search

async function dbFind(db, dbName, attribute, value) {
  let users;
  try{
    console.log(`11111111111111`)
    const users = await db.promise().query(`SELECT EMAIL_ADRESS FROM ${dbName} WHERE ${attribute} = ?`, [value]);
    // console.log(`users: ${users}`)
    if (users) {
        return users;
    } else {
        return null;
    }
  } catch (err){
    console.log(err)
  }
}


// parse the json file from front-end and save it in variable data 
app.post('/API/user/registration', function(req,res){
con.connect((err) => {
    if(err){
        console.log(err);
    return;
    }
    console.log('Connection established');
});

var username = req.body.username;
var password = req.body.password;
var invicode = req.body.invitation_code;
var name = req.body.name;
console.log('reqeust ' + req.body)

// variable initialization
var invitationCodeMatched = false;
var role = 'student';
const uid = uuid.v4();
var verifyToken = uuid.v1()
var flag = true;


// // check if the username have already been registered  isRegistered

if (dbFind.sync(con, 'login_Authentication', 'EMAIL_ADRESS', username) != null){
    flag = false
} else {
    flag = true
}
console.log(`1 ${flag}`)

// check invitation code to see if a user qualify for a TA:
if (dbFind(con, 'invitation_code', 'INVITATION_CODE', invicode) != null){
    role = 'TA';
    invitationCodeMatched = true
}
console.log(`3 ${invitationCodeMatched}`)

  // otherwisr: insert it into te database:
  const uLoginAuth = {
    USER_ID: uid,
    EMAIL_ADRESS: username, 
    PSWORD:password,
    VERIFIED: false,
    VERIFYCODE: verifyToken
  };

  const uInfo = {
    USER_ID: uid, 
    NME: name, 
    USER_ROLE: role,
    EMAIL_ADRESS: username
  };

  if(flag){
    con.query('INSERT INTO login_authentication SET ?', uLoginAuth, (err, res) => {
        if(err) throw err;
      
        console.log('Last insert ID:', res.insertId);
      });

    con.query('INSERT INTO user_info SET ?', uInfo, (err, res) => {
        if(err) throw err;

        console.log('Last insert ID:', res.insertId);
    });
  }

con.query('SELECT * FROM user_info', (err,rows) => {
    if(err) throw err;
  
    console.log('Data received from Db:');
    console.log(rows);
});

con.end((err) => {
// The connection is terminated gracefully
// Ensures all remaining queries are executed
// Then sends a quit packet to the MySQL server.
});
//send json file to the front end

console.log(`2 ${flag}`)

let judge = { 
    isRegistered: flag,
    invitationCodeMatched: invitationCodeMatched
};
res.json(judge);
//If the user has not yet verified:
lib.sendConfirmationEmail(name, username, verifyToken)
});

app.listen(3000)

The output while hearing from request is:

1 false
2 false

and there is no output of 11111111 inside async dbFind function, there is a database match in this scenario, but what it returns is :

{
  "isRegistered": false,
  "invitationCodeMatched": false
} 

which is the default value that is initailized before.