Download tar file of the splunk version that you are using and then copy paste from outputs.conf file from the same location of the extracted tar.
Perhaps if you have splunk with same version installed on any other system then just copy paste the outputs.conf .
If not then install splunk with same version and just replace outputs.conf.
You could also download the same splunk version tarball and untar it over the existing installation. This is a valid upgrade method, so it is not considered harmful. It would restore all your default settings and files back to the originals.
You need to consider if this would have any unintended side effects: are you relying on any of the values changed in the default configs. If so, you need to move them to local.