You must do this from the dos / terminal window. P4v does not accept command line commands. There is an option to "open a command window" in the "File" menu, but you still have to enter a command.
p4 -c <workspace_name> -u <username> submit -c <changelist#>
(don't use <>) By default, perforce assumes that your workspace name is the name of your computer, so if your workspace is called something else, put it in
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