Decrement Loop End for Row ⌥⌘-

Shorten the length of the loop. This command will wait for me to dive in to step sequencing again.

Logic Pro Step Sequencer overview — Apple Support

Using edit modes, you can control different attributes of the note or event triggered by a step. Some edit modes apply to only one row type, while others are common to both types. For note rows, you can change the velocity, pitch, gate time, number of note repetitions in a step, and other attributes. For automation rows, you can change the value of the automated parameter. Edit modes common to both row types include skipping and tying steps, changing the loop start and end point, and changing the step rate