Free-up space on logical volume under LVM?

I have a logical volume on an SSD drive that is filled to capacity. Both the VG and the PV are shown as full. I'm thinking I should run fstrim to free-up unused space on the LV. However, the fstrim command requires that I specify a mount point and I'm not sure what the mount point is for an LV under LVM.

I tried "fstrim -av", but this did not trim the LV in question. I also tried using "fstrim -v /dev/mapper/myLVM", but this just gives an error saying the specified mount point is not a directory.

So, I'm wondering how to free up space.

Thanks for any advice,
Eric