fix proper line for cpn backend update

doc/source/cpn/backend/index.rst

@@ -10,5 +10,5 @@ You can update the Backend by following those steps:
 1. Merge the Pull-Request
 2. Wait until the gate job has been passed
 3. Look at the Zuul-logs from the gate job. Find the line with `Successfully tagged quay.io` and remember the `:change_xx_latest` value
-4. Open a Pull-Request to adjust the kustomization config to the new tag from step 3. https://github.com/opentelekomcloud-infra/system-config/blob/main/kubernetes/circle-partner-navigator/overlays/prod/kustomization.yaml#L14
+4. Open a Pull-Request to adjust the kustomization config to the new tag from step 3. https://github.com/opentelekomcloud-infra/system-config/blob/main/kubernetes/circle-partner-navigator/overlays/prod/kustomization.yaml#L20
 5. Merge this Pull-Request and wait 10 minutes.