Outlook for Mac: How to download .olk instead of .olm

I have a Macbook Pro, which encountered problems and was factory reset. I would like to reactivate my Outlook for Mac. My mail files were saved on my mail provider's server, so I have access to them. What I need now is to regain all my contacts and calendar entries, but when I try to import files from my back-up, Outlook asks for .olm files and there are only .olk-files on my back-up disk.