Use the following command substituting your device name

mkfs.vfat -F32 -v /dev/mmcblk0

You should get an output something like this

mkfs.fat 3.0.28 (2015-05-16)
/dev/mmcblk0 has 4 heads and 16 sectors per track,
hidden sectors 0x0000;
logical sector size is 512,
using 0xf8 media descriptor, with 124735488 sectors;
drive number 0x80;
filesystem has 2 32-bit FATs and 64 sectors per cluster.
FAT size is 15223 sectors, and provides 1948515 clusters.
There are 32 reserved sectors.
Volume ID is ca5b80b4, no volume label.

Alternatively, if you don’t want to use the command line you can install “USB Stick Formatter” in your software manager GUI.