server – How can I change owner of mounted directory?

I’m using ubuntu server 20.04 on raspberry pi 4 and I want to change the owner of the external drive for changing permission for my server. But I can’t change the owner even using sudo su and chown. I changed the ownership while the drive is unmounted, but it overwrites and changes to root.

Before mounting USB flash drive on “usb128”:
[Permission and owner of before mounting to the media directory][1]

After mounting on “usb128”:
[permission and owner of after mounting to the media directory][2]

*Note: I want to change the owner during the drive is mounted.