Just a banana skin hanging amongst the plant be will release enough ethanol (or is it Ethylene the old brain struggles to recall) to help ripen the toms.
Years ago I used to wrap my green tomatoes in newspaper, put them in a plastic bag and then leave them in the warm airing cupboard.
The plastic bag stopped the moisture from evaporating and the skins therefore remained soft and pliable instead of drying out.
Do people still have airing cupboards these days??
... or on a window ledge in the sun. But learn which of the branching shoots are non producers and trim them... early and often....
I'm positive there will be no disagreement of this technique ... and I've got some beach front property I'd like to sell you... just nevermind the alligators...
Or get a ripe tomato, from the shop or a neighbour, and put it with the unripe tomatoes. You can wedge it in the plant if they're still growing on the vine.