You can book the lounge until 3 hours prior to flight departure from origin station.
Click the link below to Manage Booking (you will require PNR/ticket number/Privilege Club number and passenger's last name)
https://booking.qatarairways.com/nsp/views/retrievePnr.xhtml
Our local offices' contact details can be found in the following link
https://www.qatarairways.com/en/worldwide-offices.html