How, using Zapier, to enter the desired value in the first of the three specified empty columns in the Google spreadsheet?

Question

Google Sheets

I receive letters in which: "order number", "tracking number".
There can be up to three tracking numbers per order.
How to enter all three numbers in one line?
In other words, how to write in zapier to a column defined by the attribute "first free"?
How, using Zapier, to enter the desired value in the first of the three specified empty columns in the Google spreadsheet?