Hi, I think this should be fairly easy.
First you need to create a new event: Select the bullet sprite, select "Collides with another Object" and set the other object to be the Jump through Platform.
Then for this condition, set a new action. Again select the bullet sprite, go down to the bullet movement section, and select "bounce off object". Set the object to be the Jump through platform again.
Edit: if you don't want the bullet to bounce, then instead of selecting "bounce off object" just set the bullet sprite to "destroy"
Hope this is what you were after