mkdosfs ( terminal )

Run the below commands to format the usb to fat32 filesystem from terminal,

sudo su
fdisk -l

(this helps to discover your pendrive /dev/sdxx)

umount /dev/sdxx

then format your device to FAT32

mkdosfs -F 32 -I /dev/sdxx

Where "xx" is from the command fdisk -l which denotes your usb drive's last letters.