After preparing the new stream link, you need to create a new channel in your user bouquet and add the url. For example, when using DreamBoxEdit, this can be done like this:

Go to the list in the middle "Bouquet details".
Right click and select "IPTV and other streaming services" and then select "Add".
Select "DVB/TS" as the service type.
Write a name for the channel and add the new stream link as URL you prepared above.
Set Service Type to "1" (SD) or "25" (HD) and enter the Service ID of the original channel. You can find it in the left list ("Services") or through the WebIf.
Do NOT use the correct Transponder ID/Network ID/Namespace for the stream link. Instead, use dummy values like Transponder ID: "11", Network ID: "22" and Namespace: "33".
Repeat these steps for every channel you want to watch via the Stream Relay.