According to the documentation, the correct syntax for reloading the configuration of a TiDB cluster with TiUP is:
tiup cluster reload <cluster-name> [options]
So, to reload the configuration of the airport-tidb-pro cluster with the --transfer-timeout parameter, you should use the following command:
tiup cluster reload airport-tidb-pro --transfer-timeout=3600
Note that the = sign is required to assign the value to the --transfer-timeout parameter.