I'm taking the train from FCO to Roma Trastevre to Civitavecchia. The change at Roma Trastevre station is 5 minutes. Is that enough time to switch trains. I will only have a backpack. Thanks
That should be enough time. However, if your first train is late getting into Trastevere, causing you to miss the connection, just jump on the next train. Both legs are on Regionale trains and your tickets will be good on any of them. Those trains run at least twice/hour. Be sure to validate (time stamp) your tickets in the machines at the stations. If you don't, you will be fined and will have to pay the fine on the spot.
The starts at the airport so it should be on time. It is just a platform change and it is only two platforms so you should be OK. Write Civitavechia on a piece of paper and ask someone getting on the train if it is going to Civit.... You do not have time to go into the station to check the correct platform.