Run the following commands to download the .ova and import it
NOTE: in the example we are installing TurnKey Core
# make a working directory
mkdir ova_import && cd ova_import
# download the ova
wget -O TurnKey.ova https://laotzu.ftp.acc.umu.se/mirror/turnkeylinux/images/ova/turnkey-core-16.1-buster-amd64.ova
# extract the downloaded ova
tar xvf TurnKey.ova
# create a new vm from the ova
# usage
# qm importovf <unused vmid> <path to ova> <destination storage pool name> [OPTIONS]
qm importovf 300 ./turnkey-core-16.1-buster-amd64.ovf HDD_500GB --format qcow2