You may have received an email from the HMRC outlining if you are eligible and giving you a personal claim date. If you are eligible you have until 30 September 2021 to claim. This claim is different as it is reliant upon how much your turnover has reduced.
Covering the period from the 1st February 2021 to the 30th April 2021, the fourth grant will be available from late April 2021. Claims must be made on or before the 1st June 2021.