Update hotel room reservation array - mongoose

I'm working on a hotel room reservation system. Following are attributes in Room model.

rId: String,
        allocation: [{
            date: Number, // 210403 == 2021-04-03
            slots: [{
                type: mongoose.Schema.Types.Mixed,
                ref: 'reservation',
                maxItems: 48
            }]
        }],
        _active: Boolean

This "slots" is an array with 48 items(30mins time slots).Here I want to update this array with user inputs.As an example if a user wants to reserve a time between 2.30 - 3.30 i want to update that two slots in array to "reserved". Following code is the controller for reservation

reservation
        .save(reservation) //Save reservation data
        .then((data) => { // Update room slots
            var dt = req.body.checkInDate.substr(0, 10); // extract date from user input
            var tm = req.body.checkInDate.substr(11, 5); // extract time
            dt = dt.replace(/-/g, '');  // 210403 == 2021-04-03
            tm = tm.replace(/:/g, '.');
            console.log(tm)
            console.log(dt)
            Room.findOneAndUpdate({ rId: rId }, { //Update time slot
                $push: {
                    allocation: [{
                        date: dt,
                        slots: [{ tm }]
                    }]
                }
            })

Above code is not working. Can someone help me with this?