WinSCP offers unique feature to execute command on remote server as with regular terminal client. However as it cannot implement the terminal fully, there are some limitations. Particularly, you cannot execute commands that require terminal emulation or user input. See below for technical details.
How to Enter the Remote Command
You can enter the command on the Altap Salamander command line, while the WinSCP panel is the active one.
Technical Background of Terminal Limitations
Plugin does not support commands that require terminal emulation or user input.
Terminal emulation cannot be implemented at all as it is not possible to combine terminal emulation and file transfers in the same session. The reason is that with terminal emulation control characters have special meaning that is interpreted by the server. On the other hand the same characters (bytes) have special meaning in the file transfer protocols or may be simply present in the (binary) files being transferred.
If you happen to try execute command requiring terminal emulation, it will typically refuse to run with error message like "Error opening terminal", "No TTY available", "stdin: is not a tty" or "Couldn't open /dev/tty for reading".
Plugin may possibly support user input. However most commands requiring user input does that via terminal emulation features. If your command needs plain input without terminal emulation you can use input redirection like:
echo "some input" | command