Provided that you only have those two formats, you may try a formula like this:
=IF(LEN(A1)10,"1-" & MID(A1,2,3) & "-" & RIGHT(A1,8),"1-XXX-" & A1)
If the 1-XXX is not the same in all cases, you may need to edit the formula
to point a reference instead of the hard-coded number.

Hope this helps,
Miguel.

"Disaster Lady" wrote:

I want to change telephone numbers from format (XXX) XXX-XXXX to
1-XXX-XXX-XXXX. I also want to add 1-XXX to XXX-XXXX in cells.