I think I understand what you're asking now.
Normally you would set the Items property of the Dropdown menu to:
'[Equipment]'
But the dropdown menu can only show one column. To overcome this, I recommend that you add a helper column as you would in Excel. To do this, you will use the AddColumns() function:
AddColumns('[Equipment]',"helpercolumnname",Concatenate(model," ",serial))
- Green: name of your database
- Red: name of your helper column
- Blue: what you want the helper column to show, reconfigure this to show whatever you want
Now that you've defined the helper column, you need to set the dropdown menu to show your helper column.
Let me know how it goes.