You have to check if they are overlapping.
If player overlapping Platform
-if animation frame = 1
-If DmgCD is false
--->do the dmg
If Platform.DmgCD is false
-> Wait 1s*
-> Set DmgCD to True
The DmgCD is a boolean instanced variable that you can determine how often the player can get hurt by that platform instance. So each platform have a different cooldown, meaning you still can suffer dmg from another platform.
*you can use a Wait or you can set a Timer. If you use Timer you don't need to use the variable DmgCD. You just need to check if the Timer isrunning or not.