It can be a big job and expensive if you're not up to attempting to fix yourself. There are Youtube videos for injecting thin epoxy and clamping everything while the glue sets. The second option is to repair from the inside digging into the wall structure while leaving the exterior fiberglass in place or the third which is to completely remove the damaged exterior fiberglass. Whichever you choose what needs to happen
NOW is to repair the leak and minimize future damage. Fixing the leak won't fix the delmaintation but will stop it from getting bigger.
I did an inside repair after the stove vent fan leaked. During the effort I discovered the lower edge of the wall also had water damage and required repair. Maybe 40 hours of actual work and about $150 in material. Not difficult but you do need to be creative particularly when it comes to clamping.
https://photos.app.goo.gl/61AGFpf63y2j3gqk9
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