Given that you said you're using Update a row, I'm assuming the Excel Table already has a list of the Form IDs waiting on the amounts. Hopefully this gets what you're looking for.
For this example, I'm using the following SharePoint List.

And the following Excel Table that includes the Form IDs, but no amounts.

See full flow below. I'll go into each of the actions.

Manually trigger a flow has a single input for the Form ID. You would pass this in via your Power App.

Get items uses a Filter Query where the Title (my Form ID column) is equal to the Form ID input from the trigger.

Select retrieves the Amounts from the values returned from SharePoint. Note that for Map I've used Text mode (see arrow on screenshot).

Update a row uses FormID for the Key Column and the Form ID trigger input for the Key Value. It then uses the following expressions to retrieve the amounts.
//It's important that we include the ? in the expressions as this will ensure it returns null if there isn't an amount at that index. If we didn't include the ? then it would throw an error
body('Select')?[0]
body('Select')?[1]
body('Select')?[2]
body('Select')?[3]
body('Select')?[4]

After running the flow, and passing in 335, we would get the following output in our Excel Table.

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