I need a starting pointo to write a Views Form handler to show a Bulk Operation view field in each row instead of a single button? I have a view with a VBO field to execute a bulk operation (Get Vouchers) over nodes.

Each row has a radiobutton (I need a single selection), once you select a node you click the button "Get Vouchers" to execute the bulk operation. So far so good.

I need to show a button "Get Vouchers" in each row instead like you see in the capture below.

As Bojan Zivanovic said I need to write a  Views Form handler but I need starting pointo to write it.
VBO doesn't support that.
Furthermore, in that case you probably don't even need VBO, just write a custom Views Form handler that shows the button in each row.