Using classic Outlook for Windows in business environments
Follow https://support.microsoft.com/en-us/outlook/mail/how-to-add-and-change-an-email-signature-in-outlook
This article covers signature creation for new Outlook for Windows, classic Outlook for Windows, Outlook on the web, and Outlook.com. For Outlook on the Mac, go to Create, insert, or change a signature in Outlook for Mac.
Or, select a tab option below for the version of Outlook you're using.
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hth
Marcin