This plugin for Indigo Domotics allows you to control the pi-hole.net DNS ad blocking software with an Indigo relay switch. You can then pull this into the Alexa Hue Bridge plugin or the Homekit Bridge plugin to allow for voice control to toggle Pi Hole ad blocking on or off.
If you are using a password on your Pi Hole server, you'll need the WEBPASSWORD from the /etc/pihole/setupVars.conf file (this is different than the password you use to login in to the Pi Hole Web Console.)