int columnCount = worksheet.UsedCellRange.ColumnCount;

for(int i = 1; i < columnCount; i++)
{
    ColumnWidth colWidth = worksheet.Columns[i].GetWidth().Value;
    if(colWidth.Value != SpreadsheetDefaultValues.DefaultColumnWidth)
    {
        ColumnWidth previousColWidth = worksheet.Columns[i - 1].GetWidth().Value;

        if(colWidth.Equals(previousColWidth))
        {
            worksheet.Columns[i].SetWidth(new ColumnWidth(colWidth.Value + 1, colWidth.IsCustom));
        }
    }
}