What is the process for transferring a Thai visa extension stamp to a new passport?

If you have received a one-year extension on your O-A visa and have since replaced your US passport, you can transfer the extension stamp to your new passport upon returning to Thailand. Upon entry, present both your old and new passports to immigration to have your entry stamp placed in the new one. Afterwards, visit the local immigration office where the extension was issued, bringing both passports and any required forms and copies to complete the transfer of the extension stamp.