Short Answer 
Start your justification letter with a sincere apology for the late submission, acknowledging the importance of the deadline. Provide a valid explanation for the delay, such as unforeseen circumstances, and assure the recipient that you are making prompt efforts to submit the necessary paperwork.
Step 1: Start with an Apology
Begin your justification letter with a clear and sincere apology for the late submission. This sets the tone of the letter and acknowledges the importance of the deadline. State your regret for any inconvenience caused to the recipient due to the delay.
Step 2: Provide a Valid Explanation
Clearly explain the reason for your delay. This could include various factors such as unforeseen circumstances, personal emergencies, or technical issues that contributed to your inability to submit on time. Always ensure the explanation is straightforward and relevant.
Step 3: Assure Prompt Action
End the letter by assuring the recipient that you are making every effort to finalize the documents. Express your commitment to submit the necessary paperwork as soon as possible. This demonstrates responsibility and helps to rebuild trust.