You can only try your best and be honest when it comes to a matter like this. There are some other things you can do. As soon as you realized that it is lost, make an appointment with someone at your firm who can sign checks. This is of course if the check is coming from your company. You then need to look up the company policy of your own for replacing lost checks and gather necessary7 documents.
You should then draft a letter that formally requests the replacement check through the post. If the company requires that you use a specific format or form within your letter then make sure you stick to it. Include a business letter with your request.
You should make an appointment with the other individual involved and attend with all the documents they tell you that you need to bring. If the check is destroyed then bring the remains of the check with you to prove that it has been accidentally destroyed before it was cashed in at the bank.