How to Use AutoFill on a Touchscreen Device
To fill out a data series using your finger or stylus when using Excel 2016 on a touchscreen tablet without access to a mouse or touchpad, you use the AutoFill button that appears on the touchscreen mini-toolbar as follows:
Tap the cell containing the initial value in the series you want AutoFill to extend.
Excel selects the cell and displays selection handles (with circles) in the upper-left and lower-right corners.
Tap and hold the cell until the mini-toolbar appears.
When summoned by touch, the mini-toolbar appears as a single row of command buttons, Paste to AutoFill, terminated by a Show Context Menu button (with a black triangle pointing downward).
Tap the AutoFill button on the mini-toolbar.
Excel closes the mini-toolbar and adds an AutoFill button to the currently selected cell (with a blue downward-pointing arrow in the square).
Drag the AutoFill button through the blank cells in the same column or row into which the data series sequence is to be filled.
When you release your finger or stylus after selecting the last blank cell to be filled, Excel fills out the data series in the selected range.