Download the script in the folder where you have the nns-ifaces-0.8.0 folder.
wget https://raw.githubusercontent.com/applepiesoft/DfinityManager/main/dman.rb
or if you don't have wget
curl https://raw.githubusercontent.com/applepiesoft/DfinityManager/main/dman.rb
Usage:
ruby dman.rb <LEGACY-ADDRESS>
Make sure to use the LEGACY ADDRESS, not the public key, seed, or private key.
As a reminder, to find your legacy address, run:
echo $seed | keysmith legacy-address -f -