404 after simple change

Hi

Following a simple change in the settings of my site (lvlup.fr) via the admin dashboard; i can’t access the administration anymore and the rest of my site is on 404 error.

I understood the mistake was my own, i tried to change the site address to redirect to another page :

i was in setting , site address and changed lvlup.fr to lvlup.fr/about

and now i can’t access administration so i can’t change it to normal and can’t change it from ftp.

Could you do something about it ?