Janet wrote:
Green toms will ripen to red with no assistance; just keep them
somewhere cool so they don't dry out while you wait. My MIL kept hers
under the spare bed in an unheated room.

I've never managed to get them to ripen without turning either wrinkley and
unpleasant looking (although maybe still ok to cook with in place of
sundried??) or looking mottled and blightish.