How to change the chirality of amino acids?
Temperature is likely not going to work. To racemise something that has a chiral center, you need to break a bond: if you want to supply that much energy by heating, you are going to fry your molecule.

The easiest things to do are usually extraction of an acidic proton with a strong base, formation of a double bond involving the formerly chiral carbon, and then you go back to the initial form, but obtaining a racemate because the attack on the two sides of the double bond is equally likely.