Yikes. The proper way to fix it would be to replace the panels altogether and/or re-tile. You can't count on the tiles behind the cladding to be sound and waterproof so any bodge must be 100% water tight. If you can find a panel that matches, cut a patch to fit in the hole with a 5mm to 8mm gap all the way around, and affix it with the best silicone sealant you can find, then seal the gap and profile the silicone to the surface level, you'll have a bodge that'll last until you can invest in taking it all back to the wall and re-tiling. Make sure to seal the top openings to the corrugations to prevent water building up inside the panels.