Your description is severly lacking in describing what you want to do. But I'll take a stab at reading your mind.
To adjust the threshold voltage in a comparator circuit (trigger?), you can use a voltage divider where one of the resistors is a potentiometer.(adjustable!) that give you an adjustable "trigger" point.
If you provide your schematic, someone can provide a markup of what you need. Otherwise, its just mind reading and describing circuits with english. Good luck.