You access the Format Cells dialog box launcher from the small arrow at the bottom‑right corner of the Font group on the Home tab of the Excel ribbon.

Where the launcher is

  • On the Home tab, look for the Font group (where Bold, Italic, borders, and fill color are).
  • In the bottom‑right corner of that group is a tiny diagonal arrow button; clicking that opens the Format Cells dialog box.

Other ways to open Format Cells

Even though the question is about the launcher, in real use you have a few handy alternatives:

  • Right‑click any cell and choose Format Cells… from the context menu.
  • Press Ctrl+1 on your keyboard to open the Format Cells dialog instantly for the selected cells.

In short, the “dialog box launcher” itself is that tiny arrow in the bottom‑right of the Font group on the Home tab; the other methods are just faster shortcuts to the same Format Cells dialog.

TL;DR:
You can access the format cell’s dialog box launcher from the small arrow to the right/bottom‑right of the Font group on the Home tab of the ribbon.

Information gathered from public forums or data available on the internet and portrayed here.