Anyone can execute a rebase on Dollar Protocol. The execution is allowed at certain times of the day (see governance parameters).
Calling rebase pays the caller 100 USDx to compensate them for the transaction.
Please note: the rebase transaction is a bit expensive so be sure to set the gas limit (not gas price) to around 2M GWEI as an upper bound. The actual limit is around 1.5M GWEI but this may increase as more assets are added to the ecosystem.