Your screws are probably sheet metal type stainless with a domed head
. As you remove each screw, drop it over the side --- do not reuse any screws. They're cheap
and will more likely tear if reused. Make sure you have enough deck
thickness left and use a spade bit to redrill the hole a wee bit deeper. Use tape on the bit to ensure you don't go too deep. The point on the bit will be enough to start a new screw -- no pilot hole necessary. Put a dab of caulk in the hole and screw the new fastener home. Soak teak
bung and use a bit of gorrilla glue to hold it in place. May need a gentle tap with a small hanner to put it home. After drying, remove excess bung with sharp chisel, and sand even with deck. I generally find a bung or two missing every week as PO sanded deck and left existing bungs too thin to stay. Almost all replaced now, after two years!