The rules on who is eligible to claim have changed. However, you will still need to have submitted a Self Assessment tax return for the tax year 2018 to 2019 showing self-employment income in order to claim (unless one of the existing exceptions applies).

The third grant, which offers 80% of three months’ average trading profits, paid out in a single taxable instalment capped at £7,500, will be available covering the period from 1 November 2020 to 29 January 2021. Self-employed people who are eligible and in need of support will be able to claim the third grant at any time from 30 November 2020 to 29 January 2021.

• Check who is eligible to claim as this is different to the previous SEISS grants.

https://www.gov.uk/government/publications/self-employment-income-support-scheme-grant-extension/self-employment-income-support-scheme-grant-extension