You would need to access the browser based GUI of the router after hooking up a PC to one of the LAN-Ports.

Following the user guide Section 4.2 ( on CD or https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=2ahUKEwjrhYHbwY_eAhUEmrQKHXkgCO0QFjAAegQIBRAC&url=https%3A%2F%2Fstatic.tp-link.com%2Fres%2Fdown%2Fdoc%2FArcher_C1200(US)_V1_UG.pdf&usg=AOvVaw02xbd4TpVjjGzx0MS090O1

A video is on youtube at https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=2ahUKEwjrhYHbwY_eAhUEmrQKHXkgCO0QwqsBMAF6BAgEEAQ&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3Df_rQTzIRuqM&usg=AOvVaw3LwgC5yzuFwwvtsVfeAJnf

Again I would like to point out that this router will NOT work on certain types of connectivity scenarios whith telekom ( line type ) and other with similar product type don't even have a modem inside.

I have already done the quick setup but where should I write these anschlusskennug and mitbenutzernummer th that is the problem

There MUST be a section in the setup menu (not necessarily the QuickSetup but directly accessing the router to enter your  account data.

( there are only 2 possibilities where you do  not need to enter your data: router connect to fiber modem or your line is on a automatically configuring platform (this working only with certain other Speedport and Fritzbox models but as far as I know not with TP-LINK)

To carry on:

- pls. provide a photo of the serial number plate of the TP-LINK. This to really determine the model

- as asked for earlier pls. name the type/ name of contract you have

- complete your profile data, so Telekom team members ( not the public) can contact you and find out the physical line type if possible

- provide other screenshots where applicable

yes