You will need to take the interior handle completely off the unit. On the backside of it, there will be a plate attached that is black or brass in color. A spring connects into that plate. There will be a five-digit number starting with 1 or 2 either stamped on the plate that the spring connects into or on a rivet that holds a rod to that same plate.
Pictures are attached to help identify where that number is located.
If you can get us that number, we can source the correct lock assembly to fit your door.
Here are some examples of where you might find these numbers on the back of Trimark Locks: