try to drain some trans fluid; use a clean drain pan/container, put a quart of water in it, mark or make note of the level, dump and dry it.
pull the plug on the trans, put plug back in after you drain a quart (yeah, it will be messy - you could use a transfer pump and suck fluid up the dipstick tube)
put in a bottle of Trans-X, check the trans level, if still a little low, you have some fluid in your new clean container you can use to top-off.