to copy an specific field from a lookup - dropdown field

to copy an specific field from a lookup - dropdown field

Hi,

I have a form named "Customer" with Name, Lastname, Address, etc and I have another form named "Orders" with a lookup/dropdown (this field is named "CustomerOrder") to the first one.
In "Orders" I need to have a field with the name of the customer, then I did a Formula Field related to CustomerOrder Field, but it returns the ID of Customer and not the name

What can I do?

Thanks in advance