unable to edit content created by user 1
I think, you did not assign "edit any [contenttype] content" permission to newly created admin user, so this user does not have access to edit content created by other user.

You can follow below step for configurations.


Go to Administer ->  User management -> Permission
Assign "edit any [contenttype] content" permission to newly created admin role and save the permissions.


Kindly see that [contenttype] is content type in your website. If you want to allow newly created admin user to edit all content created by other user, you need to give permission for all content type.