Hello gamingwithpi,
add a variable to your player that holds the timespan until the next round can be fired. Then in a system event check if time is greater than the time that is stored in your variable. Right after shooting, add the amount of time you wish to wait for the next round to the current time.
if system->time > Player.timeToShoot
--> Player-> spawn Bullet
--> Player set timeToShoot to: time + amount_of_time_to_wait
time is the system expression.
Hope this helps.