Kionas leather greek sandals, size 40

Ordered these sandals from kionas sandals on etsy. They are brown, size 40. They fit my foot length-wise but unfortunately the straps are too loose (I have narrow feet). I am between an 8.5-9. The sizing chart says 40 is a US 9 and the sole length is 26.1cm. I just tried them on and didn’t wear them, so they are NWT (even though they don’t actually have tags).