Once you have the menus set up in Venue Group (you can click here for a video on setting up your Pre-order Menus in the first place), you need to go to Settings -> Venues -> select the venue you wish to add the menus or items to.
Go to the Pre-orders page
At the bottom of your existing list of Pre-order Items you will see the option to select 'Add from Venue Group'
Click this and you will see the items from your Venue Group Pre-orders will appear
Select which items you wish to copy to this venue using the tick boxes
Then click 'Copy Selected Items'
They will then appear in the list above.
Similarly with Pre-Order Menus:
Scroll down to the bottom of your list of existing Menus for this venue
Select 'Add from Venue Group'
Tick the boxes for the menus you want to copy over
Click 'Copy Selected Menus'