Bring both passports and immigration in the airport when you leave Thailand will transfer your stamp for you, just had the same situation as you few weeks ago
I had a ED visa stamp and I was done learning in the school so I canceled that visa and applied for 60 day covid extension, which I am on now, because I want to stay in Thailand.
I also have more than 15 days left of covid extension. I will go immigration office and get the requirements. Thank you.
I was on ED visa, I cancelled that already and got 60 day covid extension and now I want to get a working visa (already got a job). Just want to ask others if they have successfully changed from 60 day covid extension to working visa.