HOW TO TRIM REVERSE IN EASY WAY
When creating a new drawing, we may need to trim some unnecessary lines; in this instance, we could use the trim command, which we generally use to cut or trim extra lines.
Step: 1
SOLIDWORKS Power Trim Tool is a valuable tool. We can trim a line up to the next entity by quickly clicking and dragging your left mouse button on the line, but in reverse trim, you can extend the lines.

Trimmed line
Step: 2
So how for that “Press and hold Shift key” from your Keyboard and then “Drag your mouse on the trimmed line” See how this line has been extended so this was the reverse trim.
Shortcut key: “Hold Shift”

Extended line
It works when you press and hold shift key and then drag your mouse over the line, so that is the simplest way to create extend line.