In the liquefaction interface.

After opening a specific file, click "Filter" and select "Liquify"; after opening the "Liquify" interface, you can find the "Expand Tool" in the left toolbar. Find Filters in the menu bar and then Liquify. After opening the Liquify interface, it is the fifth tool from the top in the toolbox on the left. The expansion and contraction commands are built into the Liquify filter. You can press CTRL SHIFT X or open "Filter"-"Liquify" to see these two filters in the left toolbar.