If its new to you and came wrapped, its possible you cut the board with a knife

I used to build boards years ago and was away on holiday surfing Mount Maunganui on my 8'4" and got a fin into my board through to the EPS foam. It got me back on the water and thinking I'll do a proper repair but its lasted 10 years

No affiliations but so easy to use, bit of sanding and preparation under shade then tape clear plastic over and put in the sun to go off
SOLAREZ Epoxy repair putty is a mixture of clear, high strength, fiber reinforced epoxy resin and an amazing solar activated catalyst. There is no mixing required, just use it right from the tube. It gels in 5 seconds, curing in 3 minutes - but ONLY when exposed to sunlight.