I know how to do it in R and some other software. But in SPSS it is kinda tricky.
Maybe you saw "Homogeneous Subsets Table" in ANOVA report, you can just simply attach the alphabetical series (a,b,c) to the groups. In this regard, you will see which one is different, and easily you can type them on your column bars.
In version 27 generate the chart in the output window and double click on the chart. This will bring up an editor where you can edit many elements of the chart. You may need to select the bar, then options and either the annotate or enter textbox option. Then double-click on the new element and edit its properties to your liking.