Hi, I think what you want is what the interaction_partners API method does (you can see its documentation here: https://string-db.org/cgi/help.pl?subpage=api%23getting-all-the-string-interaction-partners-of-the-protein-set).
As you want a TSV file you have to use this URL: https://string-db.org/api/tsv/interaction_partners?identifiers=[your_identifiers]&[optional_parameters], being [your_identifiers] a string with all the identifiers separated by "%0d" and [optional_parameters] a string with optional configuration (see the link above for information about the optional parameters avalaible).
However, this method gives you only one TSV file with all the interactions for each protein, if you want to have a different TSV file for each protein you can do a loop calling the API individually for each protein.
Hope it serves. Regards