After making sure Regroover is installed correctly, open a new instance of FL Studio and click Options > Manage plugins on the top toolbar menu.
In the plugin manager, make sure Rescan previously verified plugins is enabled,
then click on Find plugins.
After the scan is completed, look for Regroover in the list by scrolling or by manually typing in 'Regroover' in the Find field.
Click on the F checkbox to place Regroover in your list of favorites.
This way it will be easier to access Regroover from the standard menu.
You're almost done!
Close the plugin manager and open the Channel Rack.
Click on the Add new channel button.
This will bring up the list of virtual instruments you can use.
Look for Regroover and select it.