Pictures are of a sliding door with the locking handle missing
Jimmy
Hello! Looks like you might just need a thumb lever. With that in mind, I would recommend our 82-107. The video below will also show you how these can be installed.
Jimmy
Gotcha, thanks for confirming. In that case my recommendation is the 82-030 handle set and 82-310 key lock (sold separately). I am very confident that these parts will work on your door and are the best picks for the job.
Now, it bears mentioning that my first thought was our 82-086 handle set. This looks identical to your original part at first glance, but you'll notice that the thumb lever on ours is in fact offset down, whereas yours is centered. Since these thumb levers can't be adjusted that means that our part won't align with yours and therefore won't work. I only wanted to bring this up in case you happened to see this set and wondered about it.