This article describes how to go from a table with Column Comparisons shown at the bottom of cells...
...to a table that places the Column Comparison letters to the right of the primary statistic in each cell:
1. Select your table.
2. In the toolbar go to Automate > Browse Online Library > Significance Testing in Tables > Show column comparisons to the right of values.
3. Press OK.
4. Right-click your table > Statistics - Cells and de-select Column Comparisons.