I think you are asking if you can convert the time from the SharePoint list to UTC Time and write it back to the SharePoint List? If this is the case you just add a update item action, and put the expression "convertToUTC" in the field you will want to write to. This will create a for each item loop that will update all of the items in your SharePoint List.
If you are putting the SharePoint List into a Variable Array, you can add the action "Data Operations Select" and select what values you want in your array, including converting that date to UTC, and then resetting the variable base on the output of your "Data Operations Select".
I hope this helps.
