First, confirm that the Google email you used to connect actually has access to that Google Ads account (check under Admin, Access and security, inside Google Ads itself). Ads Editor lists accounts with direct access as well as child accounts of MCCs: if your login has access to an MCC, the accounts it manages appear automatically, but accounts that were canceled or deactivated in Google aren't listed. If the account belongs to a different Google login, you can add more than one Google profile in Ads Editor, and accounts from all profiles appear together in the selector. If you've already checked everything, disconnect and reconnect Google to renew the authorization. If you're a team member, the account owner may have restricted which Google accounts you can see. In that case, ask the owner to give you access.