If your buckle looks like this:

you will need a new buckle https://boutiqueborealdesign.com/products/cam-buckle-with-strap-19-mm

If the Screw, washer & nut are are not in serviceable / reusable shape, then should also order:

1 x https://boutiqueborealdesign.com/products/screw-philips-pan-head-stainless-steel-nlm5-x20mm
1 x https://boutiqueborealdesign.com/products/screw-philips-pan-head-stainless-steel-nlm5-x20mm
1 x https://boutiqueborealdesign.com/products/washer-stainless-steel5-16-1-2mm

Ensure that webbing is tensioned tightly. If it's loose the webbing will break easily.

Hope this helps,