If the OMS, possibly running another platform, do not propose the Linux64 agent, proceed as follow to upload it manually:
#1 Download the following patch from MOS:
https://updates.oracle.com/Orion/Services/download/p32672601_112000_Generic.zip?aru=24165113&patch_file=p32672601_112000_Generic.zip#2 From the OMS, using emcli, run the following command to upload the patch file into the OMS
emcli import_update -omslocal -file=p32672601_112000_Generic.zip