Window sealant/filler

Hi, hoping someone far more knowledgeable than me can help.

I had some windows installed about 5 years ago by a well known mountainous windows company. From a few days after installation, the sealant/filler/caulk, whatever it is, formed horrible gaps in it. The company sent a guy around to fix it, but they never did.

Looking at the pics, can anyone offer a solution?

Many thanks

https://photos.app.goo.gl/2aZEXdmT8yZiAUMc6
https://photos.app.goo.gl/8vGDY4MrQcYZxBPJA

Those gaps are where the sealant has failed to stick to both sides of the join. I would clean out as much as I could, wipe with a damp cloth and some meths, leave it to dry and then reseal with a decent quality silicone sealant of your choice.

I would remove. Carefully cut down the silicone at edge of window and remove trim. Maybe big gap under as would not surprise me. Wind pressure blows through cavity pushing off the trim or just nothing much for it to stick to. That plastic trim can cover horrors I've had to fix. Very often after removing and filling I don't bother fitting trim back on.