Adding cell spacing to an existing cell

Thanks for your help on this. I've built a cell with text in it, and then later decided I wanted to add cell spacing so the text would be indented a bit from the side. I can't find any feature in the program that allows me to ADD cell spacing. When I looked at the html and tried to add cellspacing="10" inside the <td> code, nothing happens. Am I using the wrong code? Is there a place to edit and change an existing cell? Thank you so much. This is the code with my cellspacing code added:

<td cellpadding="5" rowspan="10" align="right" valign="top" bgcolor="#6c3809"><p>&nbsp;</p>[then it goes to text]