Follow the below steps to Install/ Uninstall Sample Data from Dynamics 365 CRM Online,

Step 1: Open Dynamics 365 Online. Goto Settings -> Data Management and click on Sample Data.

Step 2: If you have not installed any Sample Data earlier, it will show Sample Data button. Click on it to import sample data given by CRM OOB.

Step 3: After clicking on it, Goto Imports under Data Management to see the Sample Data import records Status.

Step 4: Once all the records Status Reason change to Completed, we can Sample records in the Entities Specified in the Import Name.

For an Instance, below is the Contacts Sample Data imported during this operation,

Step 5: If you want to Uninstall the same data imported during this operation, Goto Settings -> Data Management and click on Sample Data.

Then click on Remove Sample Data button.

Step 6: Records deletion status can be seen under Settings -> Data Management -> Bulk Record Deletion.

Hope you learned this feature in CRM :):):)