No one seems to have mentioned that To Ripen Tomatos Indoors
1 Put them in a box or bowl with a transparent lid (cling film/Saranwrap will do) on a sunny (or at least sun facing) windowsill
2 include an apple or a banana in the box (this provides the small amount of Ethylene (ethene) that promotes and is necessary for Ripening.
and to quote another thread, Bobs your uncle!