In Europe and Australia, you may still be able to find a 220 Volt HydroFloss for sale.
If you are not in Europe or Australia, you could purchase a regular 110 Volt HydroFloss and use this Converter:
This is the one I use when in Europe. I use mine in Germany and this converter has the correct plug for the German system. It seems that there are a variety of standards for plugs in the 220 European system and in other 220 systems around the world.
Therefore, you may need an adaptor to make it work. Adaptors can usually be found a local hardware or electronics store in the country you are staying in.
Be very careful to understand the difference between a converter and an adaptor. You may need both in some countries, but you will definitely need the 220 to 110 converter in ALL cases if you intend to plug the US 110 HydroFloss into a 220 system.
If you try to plug it in with an adaptor but without a converter you will burn it up in about 2 seconds. You might even smell smoke. So be very careful on this issue.
The converter I mentioned, I had one plugged in for years while I was staying in Germany and it worked like a champ.
Again, here is the link: https://toothygrins.net/products/simran-converter-smf-200-for-travel