Custom Firing Cooldown range

How do I make it so the firing cooldown for an enemy is a range, for example, 1 second to 1.50 seconds, that will randomly change every time an enemy attacks?

there are expressions for random values (they are listed here: Expressions reference - GDevelop documentation). You can set the firing cooldown value to RandomInRange(1, 1.5). If you use the FireBullet-behavior you can change the cooldown with expressions in the events.