How can he turn to Captain Cold when the character is dead?
Barry can go back in time to when Captain Cold isn't dead
Either Barry goes to the past to get Snart's help......when Cisco should be able to build a new cold gun......
Or the Time Storm that occurred at the end of Season 2 of Legends of Tomorrow has had some side effects......such as restoring Snart, and if that is the case then they can use that to bring RF back....
Or since Snart was at ground-zero of the occulus exploding perhaps he was blasted through time and landed in 2017