Click on the file in the upper right corner.

Then select the option.

In Outlook options, select message signature.

In the Signatures and Stationery window, under Select a signature to edit, select New.

Please enter a more recognizable name.

Then edit.

Under Select Default Signature, you can choose to use a signed account and use it in new messages or replies.

When you create a new email, you can see that the signature has been written.