It is recommended to download both certificates and register them in the web browser. During the installation process you have to confirm that these certificates are trustworthy.
The certificate of each router contains an individual "Common Name" derived from the MAC address written as "00_05_B6_xx_yy_zz". The browser points out that the Common Name of the certificate does not match the address of the called page (which is typically an IP address like 192.168.1.1). Allow the use of this certificate according to the matching MAC address which is printed on a label at the housing of your router.