Difficulty level: Pro.
The Lookup option allows you to replace old values with new ones through a Google sheet.
The file must contain 2 columns: one with current values from your source store, and another column with new values. Make sure your file contains only one sheet inside.
To use the Lookup option, follow the steps below:
Log in to Google Sheets, and prepare the relevant file with two columns.
In the upper-right corner, click Share > Copy link.
On your mapping page (Feed Mapping), scroll down to a given field (e.g. size).
From the second drop-down list, select lookup option.
Next to it, select the field to be searched for values from the first spreadsheet column (e.g. size input field).
Below, paste the shareable link to your Google Sheet file.
To apply changes, click Next and Update.
If your source store size values are set to numeric but the channel where you will be listing your items requires alphanumeric values. You can set it the same as the sample below.
It is always recommended to have a Fallback rule for products that are not matched by the condition, just to make sure that there are no empty values in your output feed.