It sounds like someone sent you a document to sign via DocuSign and they only specified your first and last name. When you click on the Signature field you may see this dialog to Adopt Your Signature. Depending on the sender's account settings, you may be able to edit the Full Name to include a middle initial or preferred legal name for signing. If that field is not editable, then you'll need to reach out to the sender and ask them to Correct the envelope to specify your preferred name for signing.

Alternatively, you might see if this option is available. In the Signing screen, there is a menu labeled "OTHER ACTIONS". Click that and choose "Assign to Someone Else".

In the dialog, enter your email address and your name as you'd like to sign the document. You will get a new request from DocuSign to sign using the updated name you entered.