An appeal against a tax assessment notice is permitted (section 347 (1) sentence 1 no. 1 AO). The objection must be lodged with the tax office that issued the tax assessment within one month of notification of the tax assessment to be contested (Sections 355, 357 AO).
Instead of filing an objection, you can also file an application for a simple amendment pursuant to section 172, para. 1, sentence 1, no. 2a AO within the objection period. In contrast to the objection, a plain amendment application cannot be extended after the expiry of the objection period.
After a final tax assessment has become (formally) final, it can only be amended under the conditions of a general correction provision under the AO or a special correction provision under the individual tax laws.