Well, clean very well the burner and especially the broken joints… flux and silver solder… no other options… Nicola
It's always a good insurance policy to clean and flux the other burner joints too, just in case they melt while you solder the flame ring holder back on.
I'm not an expert on such repairs but I would suggest that you replace the jet / nipple while you have better access because the flame ring holder is out of the way, Regards John
Yes, I am successfully soldering with castolin with 45% of silver and my basic butane torch… no risk to melt close joints…