If you MOT is due on or after 1 August 2020 you must book an MOT as usual.
Your MOT certificate will be extended by 6 months if it expires on or after 30 March 2020 and up to and including 31 July 2020. Make sure you get your new MOT before the extension expires, if you haven't already done so.
For example Your vehicle's MOT was due to expire on 3 May 2020.
This will automatically be extended to 3 November 2020 however, you will need to get your MOT by this date.
More information can be found at Gov.uk: MOT guidance