Dear thanks for the question.
First believe that it is possible to reduce 6kg in two weeks. Few things to be done
Fat free diet (avoid oil, butter, ghee, egg yellow)
Reduce
carbohydrate intake (rice, wheat)
Take plenty of water
Fill your appetite by plenty of vegetables (avoid potato)
Absolute no to junk foods
This
diet plan to be done along with physical exercises like jogging/walking (minimum 5 km) as maximum as possible.
Use some weight on your back (5 to 10 kg bag pack)
Do exercise in both evening and morning.
If you follow this religiously you will certainly succeed.
All the best for your dream of joining army.
I hope my advise will benefit you. Do write for follow up questions. Thank you.