Dehaze is not a feature of any version of Lightroom 6.
That feature is only available in the Lightroom CC. The dehaze filter was added after Lightroom 6 was released. Lightroom 6 does not receive feature updates. You can hope to see the feature added when/if Lightroom 7 is released. It will be a paid upgrade.
Dehaze is a Cloud only feature. You need CC to use it. There is no Dehaze in Lightroom 6.
Workarounds for LR6 exist using presets or Plug-Ins
Features found in LR CC and not in LR6
LR Mobile sync (other than LR Mobile trial)
LR Mobile Webspace
Dehaze tool (Effects)
Boundary warp tool (available with panorama)
Guided Upright (transform)
Selective adjustments with dehaze, whites & blacks (available with the graduated filter, radial filter and brush tools)
Reference View with active window
Filter for Snapshots or as criterion for Smart Collection
LR mobile sync recovery
As at 8 December 2016 – release of LR 6.8/LRCC 2015.8
You can actually download and add the dehaze tool to Lightroom 6 very simply from the following link:
It doesn't add the slider on the right panel but it does add a slider that is accessible from the drop down menus. Its an awesome tool. Unfortunately this version does not have the dehaze brush tool but it's still one of the most powerful tools on my Lightroom 6 now.