How to merge two audio tracks into one to be able to post it on Youtube?

When recording with OBS I have my mic and my desktop audio on different tracks. When I put it into premiere pro I can hear both audio tracks when editing but when exporting the files and posting it on youtube you can't hear both because of them being on different tracks and I don't wanna put my audio files on another app because the videos are done being edited and it would be a pain to do such. So, if you know how to make them into one audio track on premiere pro cc it would be a lifesaver. (A video of a step by step tutorial would also be amazing)  

-The file is a mov