You need to sign in using the account that purchased the file
My web partner buy the theme, and he is going to stay two months travelling by India. I need solve this before he arrive, why I have to sing with his account? I only need to know where is the slider option.
Charlie4282 is right – you need to use the buyer account. Otherwise neither the author or anyone else here is able to verify that the file has been purchased and the file has not just been downloaded or ripped.
While your case is almost certainly genuine- not only is it simply common sense and the same with any purchase of any product to require proof of purchase but also if it were a downloaded copy then the issue could well be something completely different.