Update on the covid 19 under consideration stamp for chaeng wattahana immigration.
You are supposed to return to immigration with the underconsidertion stamp. You don't need any additional paperwork.
You will get whatever number of days are left to give you a 30day extension from the date you applied. For example I went today and my visa is now extended until the 26th April and so expires before the end of the amnesty. If this is the case then you are covered under the amnesty. I was told to check the immigration website in the days leading up the the 30th for updates on the amnesty and what will be happening.
Hope this helps people.
TLDR : Answer Summary
To extend your visa at Chaeng Wattana Immigration with an under consideration stamp, you simply need to return to immigration without any additional paperwork. You will receive a 30-day extension from the date you applied, covering any days left before the amnesty period ends. It is advisable to check the immigration website for updates leading up to the end of the amnesty.