Help needed ! Transcoding 2k into 4k without using the Proxy function

Hello, I resumed the editing of a film of a previous editor and I lack knowledge on the Final Cut X software. I have to do a 4k export of a first version of the film for sending it to a festival where it will be pitched. Except that the previous editor did not use the proxy function of the software. He converted all the rushes into 2k and then imported them into Final Cut. My question is: How to connect the editing in 2k with the 4K rushes? Thank you very much !!