Two blogs with the same login — now locked out of one

I changed the home url on blackmanhouse.org to snohomishhistoricalsociety.org/wp/

Now, I can not access blackmanhouse.org because the login and passwords are the same!

(I wanted to direct visitors to the owner of the Blackman House Museum!)

My mistake was to give both blogs the same login: admin; and the same password so now I can only access https://snohomishhistoricalsociety.org/wp/
but the blackmanhouse site has all the data!
(i do have ftp access but don’t know what to do with it?!)

Help! and Thanks!