Redownloading Office

You will either have to get the optical drive fixed or fit a new one.
These days a computer is fairly crippled without one anyway, so you can't simply try and manage without.

I would take it back to the computer repair shop and insist they get your DVD drive working again. It's not necessarily their job to reinstall software (depending on what service they've done) but certainly they need to make sure your drive works (providing it's still a working drive). Again, I'm not sure what services they did for you, but they should get the optical drive working.