Top door of machine would not latch

Replaced the old latch knob and installed the new one by twisting it in by hand . That was easy. The part in the door itself was not holding the new latch knob. I tried unsuccessfully to take the door apart to install the new part that goes in the door and grabs the knob. When that didn't work, I stuck what looked like an alternative to replacing that part into the old part. It was a flexible part that was supposed to catch the knob. That worked for a while and then came out. Unfortunately, I'm back to putting a piece of cardboard between the door to make it stay up.