Ah....this I know.
You just bring it to a jeweller's shop. They will recommend a
few ways, but will take your finger measurements again to know how
much more to enlarge.
1st way: Very small enlargement, they will grind/polish internal
diameter of ring, to enlarge by at most 0.1 to 0.2mm increase in
inner diameter.
2nd way: Small enlargement, they will heat up the ring to
slightly molten state, then use of something like a thong/rod and
push it to make it with larger inner diameter.
3rd way: Large enlargement, then they will charge more, as
require more gold or silver, they will heat up the ring, then
localized make a cut, and then heat up the spare gold or silver,
then mold it to fill the cut gap, then overall heat up the ring
again, then put over rod and then enlarge it.
