Tidy all ledgers

Hi, I want to tidy up all our quick books ledgers. AP & AR

GL, 

how should I start this major task.

should it be with profit and loss? If so how can I do this on qb online?

How can I find all duplicate things entered and the type like expenses?

Plus how can I find out with quick books if duplicates in control accounts and category’s?

Sorry it’s just so different from opera and JD