Automatically fill the remainder of a cell with dots in Microsoft Excel:

1. Select the cell or cells that you want to format with dots.
2. Right-click on the selected cell(s) and choose "Format Cells" from the context menu.
3. In the "Format Cells" dialog box, select the "Alignment" tab.
4. In the "Horizontal" section, choose "Right" from the drop-down menu.
5. In the "Text control" section, check the box next to "Fill" and choose the character you want to use for the fill (in this case, a dot/period).
6. Click "OK" to apply the formatting.

Now, any text you enter in the selected cell(s) will be aligned to the right and the remainder of the cell will be filled with dots. If you need to adjust the width of the cell, simply drag the column boundary to the desired width.