When discussing hygiene you need to realize that this is a sensitive, personal issue. Make sure your tone and choice of words do not attack or degrade the Soldier. Consider explaining the impact that their behavior has on the rest of the teams (it negatively affects their morale, they could get sick, etc). Find out what the Soldier has to say about this issue.
A counseling statement could include:
“I am personally/professionally concerned about your level of personal hygiene. Personal hygiene can affect the health, morale, and safety of yourself and those around you. While I understand this may be a sensitive subject, it is also a matter of unit concern as it has the potential to affect other members of the unit. You need to improve your level of personal hygiene.”
Your plan of action should include specific tasks for the Soldier to perform. Finish with the magic counseling text. I recommend speaking with your chain of command regarding this issue.