Sealant on balcony French doors

Hi Our French doors on our Juliette balcony look like they have damp on the inside. We thought it was worth replacing the sealant. Having started this, the sealant is only holding in place a vertical pvc strip either side of the doors, which appears to have been stuck on using more sealant onto the ends of the hanging tile batons. Behind the strip is an empty void next to the door frame. What’s the best way to fill this void as this is most likely where the water is coming in? And what’s the best way to stick the strip on to the edge of the tiles? Thanks