Update Sequence property to existing records

After adding a new sequence property to an existing item type, how can i update the value for existing records in database?

It tried to update using server method

string nextSequence= inn.getNextSequence("newSequence");
Item editSelectionSet = inn.newItem("myItemtype", "edit");
editSelectionSet.setID(thisSelectionSet.getID()); //looping all records here to get current row id
editSelectionSet.setProperty("my_sequence", nextSequence);
editSelectionSet = editSelectionSet.apply();