You do not have sufficient permissions to access this page

I’ve just installed WP-security-scan and said yes to changing my database prefix; I’m now locked out of wp-admin with the ‘you do not have sufficient permissions to access this page’; the front end works. I’ve found some help here – https://beconfused.com/2007/how-to-solve-you-do-not-have-sufficient-permissions-to-access-this-page-in-wordpress/ – but have never done anything with SQL before so don’t know where to start; perhaps someone would tell me where to input the ‘update’ statement and I’ll have a go?
Any help gratefully received
Nick Garnett
site is at – https://www.cselectric.co.uk