How to install a commercial Storeroom lock

[@Greenhead24]

My storeroom lock when i turn the key to open it the lever stays open. Its a dorex fh grade 2 storeroom lock,why does that happen, so when i turn the key to test it to the left the latch stays open even when the lock is loose out the box,the locksmith had to use a master to for the building to make the lock,is it just a different type of lock ,because i never remember it doing that

[@askillthatpays]

I'm not a locksmith and am not familiar with that brand, so I don't have anything to contribute, but thanks for watching.