Reconstruct, 8pp, The user regains up to half it's max HP. If stealth rocks are on the user's side of the field the user recovers more HP (75%) and the stealth rocks are removed.
The idea behind this move is that Regirock's Pokédex entries talk about it being able to rebuild itself using rocks, and the fact it's a wall and therefore would love reliable recovery, and getting to remove rocks at the same time seems like a fitting and interesting niche. I do think this would at least give Regirock some niche usage in lower tiers, as it would be far tabkier now that it can reliably heal itself and removing Rocks, the most common hazard without being blocke by Ghosts would be quite good. Especially since without Boots you're guaranteed to take some chip damage from the rocks, guaranteeing you can heal the following turn and remove the rocks. Plus it also allows Regirock to run Sturdy and still have a chance to make use of it by healing off chip damage.
Could also have it just remove hazards in general, but that doesn't work as thematically imo, especially with T spikes and Webs.
Alongside Regirock I think you could make arguments for giving this to a lot of rock type Pokémon to improve them, and maybe the other two Regis of the OG trio, but I do envision it as a Regirock signature move.
Would love to hear thoughts on this and whether it would drastically improve Regirock or if it would just be a decent but inconsequential buff