Some folks claim they can anneal 3D printed parts. You might need some way to brace your parts to keep the heat from deforming them. Read the comments in the following videos for additional tips...
Tutorial: Annealing MakerGeeks Raptor PLA - The Boil Method - 3D Printing
Annealing PLA in Place
What's the temperature resistance of annealed PLA, PETG and ABS?