How to use the telegram.username function in telegram

limit: req.query.limit || 100,
            sort: {
                updatedAt: -1
            }
        };
    if (!checkUserAccessLevel(req.user.role, accessLevels.root)) {
        //non root user limitations
        select.deleted = -1;
        select.loginCounter = -1;
        select.settings = -1;
        select.beerCounter = -1;
        select.lastLogin = -1;
        select.lastIp = -1;
        select["telegram.id"] = -1;
        select["telegram.enabled"] = 1;
        select["telegram.username"] = -1;
        select["telegram.first_name"] = -1;
        select["telegram.last_name"] = -1;
        select["telegram.language_code"] = -1;
        query.deleted = false;
    }
    if (!id) {
        DB.User.find(query, select, options, (err, users) => {
            if (err) {
                console.error(err);
                return res.sendStatus(500);
            }
            res.send(users);
        });
    } else {
        query._id = id;
        DB.User.findOne(query, select, (err, user) => {