"Reorganize" in the sentence is in the imperative mood.
Explanation:
The sentence that is given is in the imperative mood. The imperative mood it used to give commands or orders and in this sentence the speaker is telling the person politely to reorganize the books. The imperative mood is one of three other moods in the English language. The other modes are the indicative and subjunctive. The indicative mood is used when you are recounting about facts or asking questions. The subjunctive mood is rarer and it is used to express uncertainty or doubt, and the imperative mood is used to give commands or to make requests. Other examples of statements using the imperative mood are:
