Can’t reach dashboard after messing up URLl in General Settings

Help! Please!
I have been following the book, “WordPress for beginners 2020” (shows my level of WP knowledge).
In the section on General settings (p.42), the author has an image of General Settings with his URLs ending in .local.
This seemed a good idea for distinguishing the uploaded, finished pages from work in progress.

However, it is not.
There is no /wordpress.local/ folder for WP to open such pages.
Everything comes back with our 404 page, including logging in, and the Dashboard and so General Settings where I could correct my foolish mistake back to etc.

Please would you advise how to best, with least damage, escape from this self-inflicted mess?

Thanking you in advance for your, no doubt, wise advice,

The page I need help with: [log in to see the link]

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