mkfs.msdos -F 32 -n <volume-name> /dev/sdx1
Make sure the device is unmounted first. <volume-name> is same as label. Make sure you choose the correct /dev/sdxx (use fsdisk -l to correctly identify it).
You probably shouldn't be using Trash on a vfat partition. There may be more that one partition on the SD card. Many manufacturers of flash media (cards and USB thumb drives) create special or "hidden" partitions to hold software. Examining the card with Gparted might reveal more info about the partitioning scheme.