https://askubuntu.com/questions/491104/all-folders-and-files-in-sd-card-and-usb-drive-appearing-as-locked , trying first with the SDHC drive (sda or sdb or sdc) which you can find with:

fdisk -l

The command

sudo mount --options remount,rw /dev/sdb

Might have to do it not by dev/sda or sdb, but instead by mountpoint https://askubuntu.com/questions/213889/microsd-card-is-set-to-read-only-state-how-can-i-write-data-on-it

sudo mount --options remount,rw /media/username/mountpointofsdcard

But after those attempts, it still said "error taking ownership of filesystem on read-only file system udisk-error-quark", so I tried to reformat it (the files were readable but the disk had become read-only).