Virtual finger wag ...
Shame on you!
End ... virtual finger wag.
Always, always, always leave one or two accounts set to manual that have admin level access.
Depending upon how you changed all accounts to saml and which plugin you are using, user ID 2 was the user that initially installed the Moodle and that account should be manual.
Do a DB query of mdl_user table for ID 2 to see if that still has manual.
use db4moodle;select id,auth,username,firstname,lastname,email from mdl_user where id like '2'
You won't see the password in clear text, but you can change it in /admin/cli/ IF using Moodle 3's ...
You will be prompted for a manual account username ... use the one you saw in the query above (assuming that account is still set as an admin level user)
Then prompted for the password which must meet the character settings for site.
After success, use that username,password to login and change the saml config.
'spirit of sharing', Ken