Concord Center itself or just a Concord area business/residence? The purple line commuter rail leaves from North Station (reachable by subway/trolley from South Station Amtrak) and stops at Concord Center and West Concord. Check the mbta.com site for schedules. You could get a taxi from the station to your final destination. This might be the most economical way.
Note that by road Concord might take 40 minutes or so from South Station Amtrak, maybe $65+ by taxi, not sure using Uber.