See the section "Adding, editing, and removing co-author information" in https://help.researchgate.net/hc/en-us/articles/14292798510993-Authorship for instructions. Or is the typo in the uploaded file? In this case you have to delete the file (https://help.researchgate.net/hc/en-us/articles/14293099743121-How-to-make-content-private-or-remove-it), edit it and upload again.