Here is how you do it Final Cut Pro

First, you do is go to Window and click Project Properties

On the left column, you will see Modify Setting click that

Once on there, In Video Properties drop-down menu click Custom change the size from to 1080 X 1350 and click okay once you are done.

Note: you can change the size to fit your needs try as well (1080 x 1920)

You might see a black border, if you want to fix this go to Scale and change it to 100% to 223% then the video will occupy the whole screen.

Note: if your video does not fit then you might want to experiment with different percentage to see what works for you.

the only thing left to do now is export, click the export Icon and you are done.

There is a easy to create Vertical Video that is through Blurbiz.