hard drive – How to partition a USB stick with a Apple Partition Schema?



I’ve downloaded a .iso file for installing High Sierra and putted on my USB stick.

The installation works well right now. But there is a large part of the USB unused.

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        *15.5 GB    disk3
   1:        Apple_partition_map                         32.3 KB    disk3s1
   2:                  Apple_HFS Install macOS High S... 8.1 GB     disk3s3

The Disk Utility App of High Sierra fails to enlarge the partition, like diskutil on the terminal too.

Under Windows, the format of the USB stick will not be detected.

How can I enlarge the existing partition or add a second one to use the whole space of the USB stick without losing the data on it?