Welcome to the Community, tina41.
I appreciate your interest in the Cash Flow tool in QuickBooks Online. This feature has already been added in the left navigation menu which includes the Overview tab as well as the Planner tab. Please keep in mind that files with multicurrency turned on are unable to have access to this feature.
I have here links to learn more insights about Cash Flow in QBO:
If I can be of any additional assistance, please feel free to let me know by commenting below.