To claim, you will need:
You will need to calculate the amount you are claiming. HMRC will retain the right to retrospectively audit all aspects of your claim.
You can only submit one claim at least every 3 weeks, which is the minimum length an employee can be furloughed for.
Claims can be backdated until the 1 March if applicable.
https://www.gov.uk/guidance/claim-for-wage-costs-through-the-coronavirus-job-retention-scheme