You should still be able to change the "Hover Height" visual parameter in the shape, via the Appearance floater. If it's not the case (because the shape is no-mod), simply use "Advanced" -> "Character" -> "Appearance to XML..." to save the shape parameters, then create a new shape, wear it on your avatar, and in the Appearance floater, Shape tab, use the "Import" button to load the XML file you just saved. You should then be able to change the "Hover Height" visual parameter for that new shape (last slider in the "Body" scrolling parameters list).
This is due to LL's own blunders. First, despite my warnings, they removed the possibility for the viewer to impose (within server-side clamped limits) the avatar size to the server like it could do before SSB happened. Then, to try and correct their blunder, and although, yet again, I warned them it was not the proper solution (since we needed real time adjustments to correct animation hover heights), they implemented the "Hover Height" parameter in the shape (not a real time setting, by far, and not even adjustable for no-mod shapes)... Finally, as they admitted in the end that their "solution" was inadequate, they implemented AHH (Avatar Hover Height), something I described the functioning for them from the very start (i.e. when I discovered the issue with SSB); yet, they again did it the wrong way (the *compatible* solution with pre-SSB sim servers and viewers was to implement an avatar Z *size* delta, and they instead implemented it as a delta for the pelvis height above the floor... I had to find a formula, applying a factor between the size and feet to pelvis height, to get it working in a more or less compatible way with existing RLV scripts that auto-corrected playing animations with @ahjustheight).
I'd rather not... Again, AHH is supposed to be used for real time adjustments in order to level animations with the floor (or the seat), not as a way to compensate a constant height delta for a given avatar (especially since when you change the avatar shape/outfit, the height delta also needs to change): for the latter, please use the "Hover Height" visual parameter in the shape.
And it should be considered a bug...
Alternatively to the *proper* Hover Height shape visual parameter solution, you could use a script in any of your attachments, that would set the AHH automatically for you, via RestrainedLove. Simple (and crude) example: