Quartz worktop - resin has come out

Hi, I've got quartz worktops and the resin join in one area has come out (approx. 6 inches). I thought it would be easy to find a product to replace it myself - but struggling. The worktops are white with grey flecks, and the original resin the fitters used was white with a little grey mixed in to make it slightly off-white.

Any suggestions on what product(s) would be best to allow me to 're-grout' the join?

Thanks
Daz