STVP extension

My son's dependant pass was cancelled as he is 21 years and got a STVP for 3 months.  Waiting for his student pass outcome and require to extend the STVP .  Can someone update me the process for this extension.

An STVP cannot be extended beyond three months (the only exeption: medical grounds - unfit to travel).

He will have to leave Singapore until his Student Pass is approved or he gets another visa type.