You can initialize the WordPress admin password as follows:
1. Click the [Lost your password?] to the below of the login form.
2. Enter the Username or E-mail, then click [Get New Password] to send the confirmation mail.
3. Access the link in the confirmation mail, enter the new password, then click the [reset your password].
4. Try log in by the new password.
※If the mail address is invalid, change the mail address registred to the relevant WordPress via the control panel, and then try again.