This is more docker related but should be similar to just a plain jane install. You can add your static entries to the /etc/hosts file or you can add it the the dnsmasq.d configuration file.
Create a file under /etc/dnsmasq.d, something like myhosts.conf and add the following. Keep adding entries until your done.
Find your pi-hole dns configuration under /etc/dnsmasq.d. Open the file and add the following line to end of your the configuration file.
conf-file= /etc/dnsmasq.d/ myhosts .conf
Go back to the pi-hole GUI and restart the DNS under settings/system “restart DNS resolver”.