Hello

You can use the following study materials:

• The official authority of GMAT comes comes out with series of GMAT study materials and guides for preperation it can be accessed through one single website.
• There is also Manhattan Preperation which is more preffered by GMAT takers
  
• Kaplan GMAT premiere
  

You can check out more here: https://studyabroad.careers360.com/articles/gmat-preparation-books-and-study-materials.

Hope it helps.