One way:

Format/Cells/Number/Custom #0-00-0


In article ,
EllenM wrote:

Hello,
I have a bunch of 9 digit numbers in a column that I'd like reformatted.
I'd like to remove the leading zeros and put the remaining numbers in
xxxxxx-xx-x format. For instance:
123456789 becomes 123456-78-9
000012345 becomes 12-34-5

Thanks in advance,
Ellen