I'm assuming you're on PC though you say nothing about platform or server.

It is currently disabled, so you can't. It was wrecking havok with lag, long loading screens and log in issues. Or rather, it wasn't. But the change in the coding was pulling some other issues with some underlying stuff to the surface, which were causing the issues.
They have a hot fix incoming on NA later today to enable it again, but hopefully without causing issues again. If it works well there they'll deploy it on EU, presumably and if all goes well, some time tomorrow. Until then, you just have to do without it.

For more info, read here.