need to populate a reference field if reference. record is not created yet

[ServNowDev]

I have a target table named Vacations and another table named Customer, I would like to have data transformed into the vacations table where it will have a vacations field with a number of each vacation, sometimes there can be some vacations with the same vacation number if there are multiple flights involved for eg below. I want to the Customer table to have all of the information of the vacations traveler. so i have related list in the Customer table that will list all alike vacation numbers. This means i would need a Customer table created when new vacations records are created. also a reference field to the customer table. Issue is how can I import data to a vacations table with a reference field if no records exist yet? is this possible?

Vacation Number   Airport Arrival   Arrival Date

VAC0001              JFK                      9/16/2023

VAC0001              BWI                    9/25/2023

[Bert_c1]

First, you need to create the Customer table before you can add records to it.  You could use a Business Rule defined on the Vacations tables, to create a record in the Customer table when a new Vacations record.  To do this requires both table and columns definitions. But there are example business rules in your instance that create records in some table when another table record is created/updated.