If you are attempting to use the Service Name option on the Manual Connection tab and it only displays SID and there is no dropdown box option (it's just a gray background), it's due to either not having the Oracle Client installed or having a mismatch in the bitness of the version of the tool you are using and of your installed Oracle client.
When you install our tools for Oracle (Schema Compare, Data Compare and Source Control for Oracle) it installs both a 32 and 64-bit version of the executable. The 32-bit version is named as such and the 64-bit version is not specifically denoted:
You will need to choose the correct bitness version of the tools above that matches your installed Oracle Client and then you will have the option to select the Service Name or SID in the dropdown menu: