BuildTak is great because the printed plastic really sticks to it, it pretty much solved all the problems I had with prints detaching from the buildplate during printing.
However, it does sometimes cause the opposite problem of prints sticking too much and just not detaching from the build plate.
I'm specifically not asking how to prevent this from happening - I'm asking what to do after I made a mistake and now have a print that isn't coming loose.
If you have a heated bed, bring the bed up to a reasonable temperature, then do as best as you can to create rapid cooling. If you can remove the bed, heated or not, consider to place it in a freezer or refrigerator. Obviously, if the bed is heated, you'll want to handle the bed carefully and not place it on anything in the freezer that could be damaged while it cools.
Unrealistically, pour liquid nitrogen over the bed. This may crack the bed and/or the model, as well as be all the more dangerous for unprotected users.