If the check-boxes are in fact stored in table rows, they should have a row number property that you can use. Try capturing several of them as separate elements and see how the selector is different. Then you need to find the row number of the matching text and use that in the selector.
To get the row number of the matching text, you can either use a Loop action to go through the list of Reasons you retrieved from your app, until you find the one you need, and then Exit loop when you find it. Inside the loop, you would increment a variable that indicates the row number.
Alternatively, if you can extract all of the Reasons in a form of a table, you can also use the Find or replace in data table to find the match. This will return a table of row and column indexes where matches were found. It will be stored into a variable called %DataTableMatches%. You can then get the row index from there as %DataTableMatches[0]['Row']%.
Then to pass that into a selector of the checkbox, you will need to modify the selector. See this article on how to use variables in selectors: https://learn.microsoft.com/en-us/power-automate/desktop-flows/build-custom-selectors#use-variables-in-a-custom-selector
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