//Add data
for (var col = 1; col < 6; col++) {
    for (var row = 2; row < 11; row++) {
        activeSheet.setValue(row, col, row + col);
    }
}

$("#button1").click(function () {
spread.options.allowUndo = true;
//Select a block of cells first
spread.commandManager().execute({cmd: "clearValues", sheetName: "Sheet1", ranges: activeSheet.getSelections()});
    });

<input type="button" id="button1" value="button1"/>