Nothing really, unless you trust flange extenders which I don't. If you decide to use them, do NOT use that sealant that comes with it; it's water based and can break down from continual exposure to wastewater, leak.
Setting it on a thin layer of wax is better, squished down and buttered around the edges to prevent structural damage in the event of a leak.
I get calls for situations like yours randomly. I tell people to call someone else if they don't want the correct repair to bring it back to industry standard.
Industry standard can allow the installation of a wax ring to be almost permanent, given no one takes a plunger to the equation when a clog does occur.
Floor guys/handymen/carpenters constantly do not address this issue......causing these problems. Don't forget tile guys either.