Think of operating the bolt lock as four separate steps:
Back: pull the bolt back and hold it there.
Up: press the bolt lock lever up.
Release: release the bolt to go forward in a controlled manner.
Down: release the bolt lock lever.
Now make easy-to-remember acronyms from these four steps.
To lock the bolt open, B-U-R-D (pronounced “bird”):
Back (hold it there)
Up (and hold the lever up)
Release (you will feel the bolt catch on the bolt lock)
To close the bolt, B-U-D-R (pronounced “butter”):
When you break the task down into these four separate steps, it become easy to learn, and foolproof.
I hope this is helpful.