[Observium] Manually fix bogus RRD data?

I have a router which was running glorious cisco code with a marvelous bug where the number of active ipsec tunnels kept increasing until I put a better IOS on it.

So now I have a graph where the ipsec tunnels shoots to tens of thousands of ipsec tunnels, making the long term views pointless.

Is there some easy way I can loop through a date range or similar and set the number of ipsec tunnels to some other number (like 10 instead of 22,000)?