§1. The dean presides over the college of cardinals; if he is impeded, the assistant dean takes his place. Neither the dean nor the assistant dean possesses any power of governance over the other cardinals but is considered as first among equals.
§2. When the office of dean is vacant, the cardinals who possess title to a suburbicarian church and they alone are to elect one from their own group who is to act as dean of the college; the assistant dean, if he is present, or else the oldest among them, presides at this election. They are to submit the name of the person elected to the Roman Pontiff who is competent to approve him.
§3. The assistant dean is elected in the same manner as that described in §2, with the dean himself presiding. The Roman Pontiff is also competent to approve the election of the assistant dean.
§4. If the dean and assistant dean do not have a domicile in Rome, they are to acquire one there.
Source: Code of Canon Law (Vatican.va)