Log in to the router and go to:

Services-> Services

In there make sure you have the following setting:

Let me explain the text:

dhcp-option=ff:ff:ff:ff:ff:ff,option:dns-server,96.126.123.244

This sets the DHCP option of a device with ff:ff:ff:ff:ff:ff mac addresss and then it sets the option of dns-server to be 96.126.123.244 (which is adguard dns server, you can put whatever you wish)

The mac address is listed in the admin area of the router but if you can’t find it usually the label of devices has the mac address.

If you need more devices just add more lines.

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If this helped you please please consider buying me coffee! Thanks in advance!