Are you asking where to specify custom port in WinSCP? On Login dialog:
https://winscp.net/eng/docs/ui_login

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Or do you somehow run ssh from WinSCP (How? An SSH terminal instead of PuTTY? Custom command?) and you need to pass your custom port number to it? If you are using ssh as SSH terminal or in custom command, then use !# pattern:
https://winscp.net/eng/docs/ui_pref_integration_app#client_path
https://winscp.net/eng/docs/integration_putty#win32-openssh
https://winscp.net/eng/docs/custom_command#patterns

I have changed my port number to ???. But in order for me to ssh into it I have to put -p. So to log in on PowerShell I type in ssh name@ipaddress -p port number. So how do I get WinSCP to do it automatically?