Use this article to setup your Raspberry Pi if you haven't already.

Use the Smart Home Alexa skill or Google Assistant action.

Use a line like this in your /root/.TRIGGERcmdData/commands.json:

{"trigger":"PiHole","command":"/usr/local/bin/pihole_on_off.sh","ground":"background","voice":"ads","allowParams":"true"},

This is the bash script I wrote to /usr/local/bin/pihole_on_off.sh and made it executable with chmod +x /usr/local/bin/pihole_on_off.sh

#!/bin/bash
case "$1" in
  "off")
    pihole enable
    ;;
  "on")
    pihole disable
    ;;
  *)
    echo "Run this with on or off as the parameter."
    exit 1
    ;;
esac

This page gives a list of pihole commands:|
https://docs.pi-hole.net/core/pihole-command/