Taping the seal on three sides is supposed to allow air to escape while blocking air from sucking in. In my experience, that doesn’t really work so well. Blood tends to glue the plastic to the wound.
Careful observation works much better than improvised chest seals. Just watch for signs of pneumothorax and remove the seal if necessary. There are chest seals made specifically for sucking chest wounds, but nothing beats careful observation.
If you do have to remove a chest seal to relieve a tension pneumothorax, you probably should leave it off. Removing the seal will most likely let the pressure out and equalize the pressure inside the chest with the outside atmosphere.
Again, watch the patient closely for signs of tension pneumothorax. Recognizing one is difficult if you haven’t been trained in first aid.
If you have a patient with a penetration wound to the chest of any kind—industrial accident, gunshot wound, stabbing, etc.—the most important step is getting professional emergency medical help.
Don’t hesitate to call 911 or get the person to the emergency department as quickly as possible.