It's a ridiculous claim. The Republicans and Democrats already had official, above-board access to the electoral roll data, and it's not sufficient for even the most basic campaign let alone micro-targetting. Political parties put a huge amount of effort into augmenting that data with the information they need to actually run their campaign, sometimes literally sending volunteers door-to-door to ask voters. This is how campaigning has worked since before Facebook even existed.
The whole idea that Republicans and Russians conspired to do micro-targetting with voter rolls basically preys on people's cluelessness about how political campaigns work and their willingness to believe anything that involves Trump and Russia stealing the election. The fact that it wouldn't work and makes no sense doesn't matter.
