The original one had broken, so a replacement has been bought. The original had just the one ribbed soft sealing ring, the replacement had two, but no instruction for assembly.
One of the rings has a ring of ribs around it and will fit above the hole in the sink, or below - the other is completely flat slightly thiner and its internal diameter would need to be stretched to fit above of below the hole in the sink which would make assembly difficult.
Is the latter seal just a spurious part?
Does the ribbed one fit above the hole or below?