connect clients to there previous account when they book again

At this point I, when I get booked again by the same client, they use the booking form like they did when booking the first time. Now I got booked for the 3rth time and have the same client 3 times in my system. Would be amazing if I would be able to except the request and connect them with a previous already existing client and make it automatically seem as one client without losing any of the data.