First upload your products to EMERGE App, then prepare an excel file (please use the file that you find under Products > Product Actions > Import Product) with SKU and columns you need to update and talk to our support agents to ask for data update.
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e.g If you want to add multiple categories, prepare a sheet with 2 columns and up: SKU, category 1 category 2, etc.. (screenshot of the excel)

So the same thing with other fields you want to update, need to make sure they’re not available in the original sample file