Need help getting other computers to use pi-hole

Apologies for Noob questions. I recently installed pi-hole on my Pi 4 and it seems to operate fine on the Pi. I have two other OSX computers that connect via wifi to my router and I would like them to benefit from the pi-hole too.

The router is badged Fastgate from my ISP, Fastweb in Italy, and it does not appear to let me do anything about DNS. It does allow me to deactivate DHCP.

I don't really understand how to set pi-hole to provide the DHCP or how to get the Mac computers to use the pi-hole exclusively. I would welcome step-by-step instructions if there are any available.

Thanks

Debug Token:

https://tricorder.pi-hole.net/aspcyxnhqa

You also have the option of manually assigning the Pi-hole as DNS server on the Macs. System Preferences > Network > Advanced > DNS.