Hi Marta (@Komsa)!
For future invoices, you can add your tax identification in Address Line 2. Please access eSignature Settings > Account Profile > Account Address. Check this article for more information: Update Your Account Name and Address
For invoices already created, I’m not sure if Docusign can edit them. My recommendation is to open a case with Docusign Customer Support and ask them if is this possible. To open a case, please follow these steps: Open a case in the Docusign Support Center
I hope I could clarify your question!