Look at the Chinese Embassy Bangkok website for the company that does their visas.
I did similar for a friend with the Chiang Mai Embassy.
You will fill in an online form and give it all to the visa company.
You need to get an online reservation for meeting the visa company staff, so do this first thing….you cannot just walk in.
Gather your documents beforehand as this makes the process easier.
They seem to only accept single entry visa .
Make sure you have a local Chinese person who will be your contact there. Name, address, phone number.
Make sure you have a sample itinerary along with your flights in and out purchased (you can try to get refundable tickets). Also provide all of your hotel reservations ( again get them as refundable).
Upload all of this to the online visa form. Plus print out all the above information to attach to your application. Make an extra copy of everything…..
Once you get your visa and go to China, you will need to fill in the paper Arrival Card.
Do it very neatly!
Immigration gave me a hard time because of messy handwriting. They wanted to see all of the reservations so have them handy.
Also you will need to fill out the health decoration form just before departure to get your health qr code.