Disassemble and remove anything attached to the carriage

Your linear rail may have a small plastic “stop” at each end. These are usually red. This is to prevent the carriage coming off of the rail under normal use.

Carefully grip the plastic stop as close to the rail as possible. You may find it beneficial to use a small pair of flush cutters to do this, but don’t cut the insert!

Pull the stop out of the hole in the linear rail

Slowly slide the carriage off the end of the rail, gripping both sides as you do so. Set the carriage to the side, making sure to note the orientation it came off of the rail.