You should say:

• What you lost
• When and where you lost it
• What you did to find it
• And explain how you felt about it

Sample Answers: https://ieltsquangtri.com/describe-an-occasion-that-you-lost-something/

You should say:

• What the contest/ competition is about
• where the contest/ competition will take place
• When it will be held.
• And explain why you would like to participate.

Sample Answers: https://ieltsquangtri.com/describe-a-contest-or-competition-you-would-like-to-participate-in/

You should say:

• What it is
• How it helps you concentrate
• When you do it
• And explain how you feel about it

Sample Answer 1: https://ieltsquangtri.com/describe-something-you-do-that-can-help-you-concentrate-on-work-or-study/