You need to make a distinction between Conditions and action.
The cooldown is part of the condition not an action, so you should not use the Wait action.
There are 2 ways to make the cooldown.
First method is using instance variable.
Add Instance Variable to the player, lets call it PlayerCooldown. Its value should be zero on default.
The player can shoot if the PlayerCooldown < 0 and lmb is pressed.
When he shoot, the PlayerCooldown value will be set to Value X (in seconds)
Make another event that will reduce the PlayerCooldown value to zero. An event condition like Every X seconds can do the job, Make it so Every X seconds, X value of PLayercooldown will be substracted.
Method 2, make use of an add-on created by rexrainbow