You need to create a script i Script Workspace. This script should be something like this
Set Variable $Field1 to value from Field1
Set Variable $Field2 to value from Field2
Set Variable $Field3 to value from Field3
Set Variable $Field4 to value from Field4
And more if you have more fields
Go to layout (your other layout)
Create new record
Set Field (Field name 1) to $Field1
Set Field (Field name 2) to $Field2
Set Field (Field name 3) to $Field3
Set Field (Field name 4) to $Field4
You might also want to consider whether you actually need to duplicate the information, or whether you can access the necessary information through an established relationship. In FileMaker (and other relational database systems), it is often preferred to use a relationship to access related information rather than making copies of the information. A form (or layout) can access information from related tables.
From what you describe it seems to me that it would be better to have a User or Client table that stores the user/client information, and then a separate InventoryItem table that tracks the individual inventory items. If you could explain a little more about your system, we might be able to help you think through the best structure.
With properly established relationships there is usually no need to have data in more than one place. That's why it's called a Relational Database.