Use the `LOWER` function: `=LOWER(A1)`
Enter the formula in a new cell
Replace `A1` with the cell containing the uppercase text
Press Enter
Copy the formula down for other cells if needed
Copy the results and use Paste Special > Values to replace the original text if needed
Use Flash Fill if the pattern is simple and Excel recognizes it
Use Power Query and transform text to lowercase for larger datasets
Use VBA with `LCase` for automated conversion across many cells