>>14584489fly to Poland or Romania and get a bus as close to the border as possible.
You probably could hitchhike your way in. Lots of Ukrainians are coming back to fight so I think if you get a paper sign saying “I want to fight against Putin, take me with you” in Ukrainian then Dima or Volodymyr will take you with him. Then just let him do the talking.
Make sure that it’s legal in Greece to join the foreign army.