The standard procedure in heavy icing is to leave the FL that is causing the problem. If that leaves you below safety altitude or above your performance ceiling then you have left it a bit late - declare an emergency and get radar vectoring towards your nearest suitable airfield.
Prevention is a lot better than cure - most aircraft considered fit for flight into known icing conditions will have a weather radar fitted - this will be used to avoid areas where severe icing is likely.
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You know when you've been CHF'd!