Need to add parameter in SDP

The INVITE message sent to provider has SDP need to be modified :

The below SDP is missing a=sendrecv

I need to add this a=sendrecv in the SDP .Please help to achieve this.

v=0
o=- 0 0 IN IP4 10.53.33.66
s=session
c=IN IP4 10.53.33.66
b=CT:2500
t=0 0
m=audio 53018 RTP/AVP 102 9 0 8 97 13 118 119 101
a=rtpmap:102 opus/48000/2
a=fmtp:102 useinbandfec=1; minptime=10
a=rtpmap:9 G722/8000
a=rtpmap:0 PCMU/8000
a=rtpmap:8 PCMA/8000
a=rtpmap:97 RED/8000
a=rtpmap:13 CN/8000
a=rtpmap:118 CN/16000
a=rtpmap:119 CN/24000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=maxptime:200
a=ptime:20