Clean out all that adhesive, whatever it is, and lay down fiberglass mat with resin. It's messy and sticky, and itchy and requires a mask when sanding (you really don't want fiberglass dust in your lungs). Really, it's super itchy so gloves and long sleeves are recommended.
Read up on fiberglass repair. It's not that it's difficult, just time consuming and intimidating.
Unless it starts showing signs of failure, do as others have said, leave it be and continue as you had before discovering the damage.