Assign key to tab through Layer Composition/Blend modes

What is the process to assign tab or arrow down through composition modes? At some point in the past I linked my down arrow key to Layer Composition/Composition Mode? (since i can’t seem to remember the blend mode calculations, I just run through them. I know I’m not the only one who does this ;-) But i’ve forgotten how to assign my keyboard down arrow to the next composition mode. Please help?

Click on the composition mode, in the button UI, click the Nav Tab, then set the up and down arrow to Move Up and Move Down.

You may have to select the other blend modes as the up down will move the default list first (which is just two comp modes).