In old QBO:
From the home page screen > select company > select export data
In new QBO:
From the home page screen > select company gear (upper right corner) > select tools select export data
It goes through two phases with several steps within each phase. It is not a seamless process. Use Internal Explorer for this tasks.
For details, read these articles:
https://qboe.custhelp.com/app/answers/detail/a_id/4682/kw/4682/r_id/103898
Also, be familiar with all export limitations before this job.