Hack Attack To My Site

I got an email from google today. it says my site is under attack and there is some pages that from attacker.

after i saw this i immediately updated my WP tp the last version. but i think it was to late now.

i can’t delete the page because when i login with my admin acc the page is not openin it is given me 404 error. but when i open the page like visitor then it is opening.

how can i delete this, what can i do?