As the form is different for each tax office (Finanzamt), we cannot provide you with a generally valid template.
You can easily download the form from the website of your tax office.
This is how it works:
Find your local tax office on the internet using the search term: "SEPA-Lastschriftmandat Finanzamt [name of your Finanzamt]"
Fill out the form completely
Print out the form and sign it.
Send the original printout to your tax office
Some tax offices already offer the option of filling out an online form and/or sending it by e-mail. You can find more information on the website of your local tax office.
If you have any questions or need further information, please do not hesitate to contact us.