When I check with line feed code conversion, tr often appears, but there were cases where specifying the line feed code was tedious & conversion did not work. If you look for something easier, you can easily do it with nkf.
Since the environment is Mac, the default is line feed code LF
$ file sample sample: ASCII text $ od -c sample 0000000 a a a a a a \n b b b b b b \n c c 0000020 c c c c \n 0000025
$ nkf -c sample > sample_CRLF $ file sample_CRLF sample_CRLF: ASCII text, with CRLF line terminators $ od -c sample_CRLF 0000000 a a a a a a \r \n b b b b b b \r \n 0000020 c c c c c c \r \n 0000030
$ nkf -d sample_CRLF > sample_LF $ file sample_LF sample_LF: ASCII text $ od -c sample_LF 0000000 a a a a a a \n b b b b b b \n c c 0000020 c c c c \n 0000025