What should I do if I was mistakenly stamped with a 30-day tourist visa instead of my non-immigrant visa upon entering Thailand?

If you accidentally received a 30-day tourist visa stamp instead of your non-immigrant visa upon entering Thailand, the best course of action is to visit the immigration office at Chiang Mai airport to have the stamp corrected. It's generally a straightforward process, as immigration officers can rectify the error. Alternatively, you can choose to stay until the tourist visa expires and then exit the country to activate your non-immigrant visa upon re-entry.