Format Xbox One flash drive USB format tool
Partition Expert Can do more than just resize and move partition without data loss, Format USB or any other external hard drive with ease is also one of its features. As we can informed by Microsoft Xbox One's guide page:
To update or repair an Xbox One console from a USB flash drive, you'll need a 4-GB USB flash drive formatted to NTFS.
1. Right-click on the USB device and select Format Volume.

2. Set File System to NTFS and click OK, and then Commit it.

About Xbox 360
Steps above are also applying to Xbox 360, but not format to NTFS file system, FAT32 instead:
To use a USB flash drive with your Xbox 360 console, it must meet these requirements:
- A minimum of 1 GB of storage capacity
- Windows FAT32 file system format
if you are using FAT16 and NTFS, here's the official advice:
Note If you formatted the device in Windows using FAT16 or NTFS, you might be able to reformat it in Windows using FAT32
We're using NTFS actually and we know 'format' courses data loss on the NTFS partition, we have alternative plans:
1. In Partition Expert, we right-click on the partition with NTFS file system.

2. Choose Convert to FAT32 and click OK, Commit.

By doing this, we get a partition with FAT32 file system from NTFS without damaging data stored in it.