The Potion of Restoration is a special potion introduced in the Blood and Wine expansion for The Witcher 3: Wild Hunt. It allows the player to redistribute their ability points that were used for mutations but it does not return the mutagens used, so you'll have to re-gather them to unlock any abilities.
The following merchants can sell it:
- herbalist at Coronata Vineyard (after being rescued)
- herbalist just east of Lazare Lafargue in Hauteville