Export video for smartphone

[UrlSepp]

hi Guys,
I recorded a video with my cell phone (upright), which I would now like to cut with shotcut.
How do I correctly extract the video that I have no black borders left and right.
If I change the aspect ratio when exporting from 16: 9 to 9:16, then I suddenly have black borders on the left, top and bottom.
Does anyone know a tutorial on this?

many thanks, greetings,
Sepp

[shotcut]

Choose one of the vertical video modes at the beginning of your project:

Video Mode

Introduction Video Mode is the project resolution, aspect ratio, frame rate, and color space. It is important to set this as you desire at the beginning of your project. If you try to change it later Shotcut will try to retain the timing of edits, but some users have reported problems, and it is risky. Also, at this time Shotcut will not automatically adjust anything for you related to size and positioning of elements like text and picture-in-picture when changing resolution. You can think of…

[UrlSepp]

I tried it, worked perfect for me !
Thanks !