to do this you would need to use the continuous delivery feature in IBM Cloud to add you node's files to the git repository for your application. You should put the files under the existing nodes directory. Then make sure you add any npm dependencies your node has to the package.json file. Once you commit those changes and push them back, the delivery toolchain will run and redeploy your application and your nodes should be available.
If you ssh into the running application and copy the files over, you are updating the current running instance. The next time the application is restarted, any changes to the filesystem will be lost as the image reverts back to the built image. This is why you need to make your changes in the git repository because you need them to part of the build image.
This is not specific to Node-RED - it is how you work with Cloud Foundry applications (CF being the environment you have Node-RED deployed in as part of IBM Cloud).