If you have not already done so I would encourage you to have an open and honest discussion to find out the root cause of the problem. If you show a sincere desire to understand and correct the issue you will probably get a positive response from the Soldier. You do not have to do this but it shows you care.

"To be a good leader, you must be a good follower."
There are several methods to correct a negative attitude. In this case I might suggest the following: Have the Soldier go to the post library or public library and check out a book called Over the Top by Zig Ziglar.
Comments
David
After intergration of the South African Armed Forces(SADF, MK, Apla, Transkei, Sickei,Venda and Bopotaswane) there was a visible and dramatical change in the behaver of newly enroled soldiers.
Lack/poor disipline.
Negitave/poor attitude.
No sence of responsibility even during
operational deployments.
No trust towarts leadership.
Quesion?
1. What can the underlined reasons be for the sudden change of their behaver/attitude.
2. What possible solutions can be used to rectify it
Part-Time-Commander
Here are a few things you can do to fix a Soldier’s attitude.
1. Make sure your attitude is squared away. Set a strong personal example.
2. Have a heart to heart with the Soldier. Sit down and tell them what you think about their attitude and ask them “why” they are so negative all the time.
3. Assign the Soldier a couple books to read about “attitude.” Have them write a report about what they learned.
4. Praise your Soldier when they have a good attitude. Don’t always focus on the negative.
5. Accept that some people are naturally negative and cynical.
I hope that helps.