There are numerous options; you can reset, switch to triples (doing 2 sets or 1 heavy set and 1 back off set of 5), do multiple sets of doubles or singles, alternate Rack Pull and Halting DL as a heavy pulling movement...
However I think we can help you better if you give us a bigger picture of your training.
Have you tried to to pull the 5th rep? If so, where do you fail? What is the limiting factor?
How do your RDLs and Squats go? As far as numbers, volume, progression.