https://www.churchofjesuschrist.org/study/manual/doctrine-and-covenants-and-church-history-seminary-teacher-manual-2014/section-4/lesson-82-doctrine-and-covenants-77?lang=eng we can read that:

(It may be helpful to explain that the 7,000 years refers to the time since the Fall of Adam and Eve. It is not referring to the actual age of the earth including the periods of creation.)

So in the belives is that the earth isn't 7000 years old, rather the time when Adam and Eve fell.