@Vanny *****
I’ve done it at Chiang Mai lots of times. Get your document from the helpers, near front doors immigration. They have a copy house at the back of the building to copy passport etc. They can also take your photo there. Fill in your form while you wait. Whole process takes approx 1 hour. They close between 12:00-13:00 for lunch. It’s best to go when it opens in the morning or, at 13:00, when it reopens after lunch.