They won't really have to do anything really - the sites that don't have age verification will rise in the search rankings becoming easier to find. There are a multitude of web browsers/add on apps that circumvent the age checks too - these will just rise in the ranks/become the normal tools that will be advertised to people who are searching for porn.
For most it just means that they either the underage/privacy minded porn hunter will use a VPN/free browser to circumvent, or they'll avoid the 'mainstream' websites. The mainstream websites which will be the only ones that sign up to age/id checks are the ones that generally have some kind of standard that makes sure those features are not underage and are consenting.
This means that the kids actively looking for porn will be more like to access the worst sites plenty out their advertising ex-girlfriend vids, underage vids, drunk girl vids - they're not going to be asking for age verification are they.
It's all horrific. But this change will either be meaningless at best, most likely harmful. It's a massive boon for the worst of the porn sites because they're the ones going to be getting the extra traffic, extra money for them.