https://github.com/HQ20/contracts/blob/4c4acb1328d35659f18f10f0bcdcd54a74071c31/contracts/access/Hierarchy.sol#L15 _grantRole() in AccessControl.sol is current private, so cannot be called by child contracts. [See here](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/AccessControl.sol#L183)