Please help me to correct these sentences?

The Principal,

SNV School

Sandra, Mumbai

Sub. Request for time extension to submit vaccination history details.

Dear Sir,

As we don't have the vaccination history details here in Mumbai.we can't provide it at the moment, but we will submit the details next working day.

Therefore, we request you to allow us for a time extension in order to submit the documents next week.

Thank you for understanding.

Yours faithfully

Parent.