All you can do is going to apply for another one. The process is same. Processing time is not that long, but you have to wait for how long it would take. Or you can book a queue online.
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You cannot choose the immigration office because it's close. You have to go to the specific office.
IF you bought the tourist visa BEFORE you came to Thailand and were stamped for 60days, or you had any Non-immigrant type visa, you would go to the main office at Chaengwattana Government complex building B.
IF you didn't buy any visa before your travel and just came to Thailand for free (visa-exempt or visa waiver) or paid for Visa On Arrival at the airport when you arrived, you will go to IT Square Laksi Plaza temporary office.
Attached is the general information for the Covid extension.
As you had multiple Covid extensions already, prepare the documents as much as possible.