You can open it by putting it with low Temp in the oven (50°C), the sealant/glu will get smooth.
The other opportunity is to remove the LED Flash-/Daylight Module after dismount the Headlight. That is only hole you can use without removing the glas. You could try to get the water out and dry it with warm (not hot) air.
But removal (of the Headlight) isn't easy, because the bumper has to be removed and the lower part of the headlight is fixed behind two bolts, that can't be removed without drilling.
So if you have an insurance that pay for it, go to your local Vauxhall dealer to replace.