show your debit transaction from your foreign bank date and amount, show the same going into your Thai account with whatever Thai paperwork you can, any reasonable officer will accept this one off paper trail as evidence.
typically you need to satisfy the 800k requirement for your first extension, you'll need to ask the immigration office you'll be using if they will accept the monthly method for the first extension without an embassy income verification letter. I may be wrong on this.
if you had to do a second consecutive report, you'd be at immigration in person getting an extension and the officer would do it for you, or you'd be illegally on overstay in the country.
Have you submitted the application and paid the fee? If so, you're out of luck. If you haven't paid yet, then just let that application expire, the system will delete it in a few weeks. Meantime start a new application in your evisa profile.
You'll need to send a minimum of 65,000 Baht each and every month for 12 months from abroad before you apply for your next extension at the same time keeping all the requirements for the 800,000 banked method.