You can refer to this article to see if the previous operation was successful.
If it is still not work, please try:
1, Login you SharePoint Online site with Internet explorer [IE] then try to login the SharePoint Designer 2013.
2, Try to uninstall SharePoint Designer and then install again.
If the problem still exists, to help you better, we suggest you can open a ticket to contact Microsoft for more direct help.
Thanks for your understanding.