In order to check or adjust the configuration settings you need to open the router's configuration website. The address is printed on the back of router or can be found in the manual. The configuration website likely has one of the following addresses:
Use the login data printed on the back of the wifi router for access to the configuration website, if you have not already changed the login credentials.
If the website is not accessible anymore, you might need to restore the factory default. Instructions on how to do that can be found in the router manual.
Select the Advanced settings (if available).
On the menu left go to Network → Internet or Network → WAN.
The Internet Connection Type needs to be: Dynamic IP.
If that is not the case, please proceed as follows:
Depending on router type and software version, the configuration interface looks a bit different.