def METHOD_NAME(existing: list[str], new: list[str]) -> list[str]:
    converted_names = []
    unique_names = list(new[:])
    for i, n in enumerate(new):
        if n in existing:
            original_name = n
            fixed_name = n
            duplicate_count = 0
            while fixed_name in existing:
                fixed_name = n + "_" + str(duplicate_count)
                duplicate_count += 1
            unique_names[i] = fixed_name
            converted_names.append(f"{original_name}   ->   {fixed_name}")
    if converted_names:
        import warnings
        ws = column_name_conflict_doc.format("\n    ".join(converted_names))
        warnings.warn(ws, ColumnNameConflict)
    return unique_names