Write a letter to the admissions tutor: explain your position apologise and offer to come on another day or later the same day. ask how long the interview will be and whether there will be any tests during it.

Dear Mr. Smith, Thank you for inviting me for an interview in the prestigious organisation. After recieving the invitiation, I was very excited and happy. Closely looking at the invitiation, the date on which the interivew is scheduled made me little unhappy and triggered the thought of dropping a letter requesting to re-scehdule the discussion rounds. Unfortunately on 15th March 2021, I have function in the family as my real sister is getting married. Being the only son, I have many responsibilities which I need to attend such as greeting relatives, making sure all the arrangements are perfect, everyone is confortable and have checked into there rooms etc. Henceforth, I will not be able to come down for the interview. Therefore, consider the letter as my appology and will like to propose a different date for the discussion rounds. I did think about dropping by in the evening but found it too exhausting. Thus, I will like to request you to give me another day and time to have the interview. In addition, If you could also include the number of rounds like an apptitude test and basic expectation in each round from the candidate will be really helpfull. Looking forward for the revised invite. Yours Faithfully, ZYX