This should replace all carriage returns or linefeeds with a space in a field named myField:
yoursearchhere
| eval myField = replace (myField, "[\n\r]"," ")
| morestuffhere
If your data is from Windows and has CRLF in it, this will replace the CRLF with two spaces.
A refinement would be to make the regex "[\n\r]+" which would see one or more carriage returns or line feeds (or any combination thereof) with a single space.
do you have more than one carriage return in the field value??