Usually the phrasal verb **look up** is used as follows.
These example sentences are from the Oxford Advanced Learner's Dictionary.

>Can you look up **the opening times** on the website?

>I looked **it** up in the dictionary.

The objects of the phrasal verb in those above sentences are what are actually needed to be found.

Suddenly, I saw this sentence from an English learning material which is not popular and this sentence was there alone so there is no context I can add here.
>Look up **the dictionary** if you have trouble translating.

As ***the dictionary*** in that sentence is not something searched for but something used as an instrumentality to search for something else, I somehow feels the sentence below is more correct.

>Look up **in the dictionary** if you have trouble translating.

I would like to know what is right and wrong.
Thank you.