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