First of all, be confident and humble at the same time. Accept your mistake by saying that you have done something wrong. In this way you prove that you are a sincere and professional person.
Make sure that you do not give lame excuses by saying that the mistake happened by chance or something like that. It will not convince others and they will not trust you anymore.
Along with accepting your mistake, make an official apology to your staff members. Say that you are sorry for making the wrong decision or for committing the mistake.
Do not try to put your mistake on anyone else or involve any outside factor. Take full responsibility and show your determination to resolve the problem in time.
Accept your mistakes as soon as you discover it. Do not waste time as it can make things worse at a workplace and can cause bigger loss.
Try your level best to fix the mistake as only accepting your blunder is not enough to resolve the issue. If you cannot fix the problem, then seek help from others who can assist you in this regard.
The most important thing is that learn from your current mistake which will help you to avoid repeating it.