Hello, according to the regulations of the airline, if you cancel the first-leg train ticket and directly take the second-leg flight from Tianjin to Fuzhou, it is usually OK. However, for specific circumstances, you need to consult the airline or ticket purchasing platform to confirm whether there are relevant refund or change fees, and whether you need to provide corresponding supporting documents. It is recommended that you contact relevant service personnel in advance to understand the specific operation procedures.