reset DNS settings to default

Hi,

for what reason ever I entered manually my router address in the DNS WiFi settings and Search Domain.

That works all fine... but only @home.

If I connect in an other Wifi now, the system is not running. Also clear, because my local router IP is different from the one in the other network.

But how can I reset it to default and that I receive again the DNS settings from the network?

All searches in the inet shows me how the flush the DNS cache but not this topic.

Thanks