TurboTax does not automatically populate the amount you received for the 3rd stimulus payment - as you noticed when you needed to input the amount. Instead, it assumes your payment amount is $0 (since the box is empty until you populate it) and estimates the full amount included in your refund. When you complete the box with the amount you already received, it is merely removing that amount from your refund to properly reflect that you already received.
But when i put tan amount then my refund changes to me owing the $2,800 which seems wrong
No, it starts with giving you a $4200 refund. Ignoring all the other items of your tax return, you then enter that you received $2800 already. It deducts the $2800 from the $4200 showing a refund of $1400.
It is not taxable and you aren't paying it back. Your 2021 return starts out by assuming you didn't get any Stimulus payments so it gives you credit for the full amount and your refund was too high. Then near the end you enter how much you actually got so it only gives you the difference if any. So you don't get it again.
If you are filing married jointly and have 1 dependent then 4200 is the correct amount. Did you get the 4200 third stimulus payment last year ? Did the IRS only send one spouse the letter stating 2100? If so you still had to enter the 4200 you actually got even if you did not get the second person's reminder letter. So if you had a credit on line 30 of the form 1040 and you did get the full credit in advance then the IRS would adjust the return accordingly ... you can either have the credit or the advance but not both.
Filing jointly with 1 dependent. Never go the letter from IRS as it was lost, but checked on IRS.com and it says I got $2800 although do not see a $2800 IRS deposit that on my bank statement and went thru all of 2021 nor do I have a check stub. My return never started with he 4200 refund so when I put in the 2800 it then goes from a refund to an amount I owe so how can I see if the return is starting with the 4200 refund? Do I need to start all over or remove my W-2's?
Turbo Tax started out giving you the 4200 as soon as you entered your dependent. If you didn't see a big refund in the monitor it was probably just deceasing a tax due you had and showed you a smaller refund.
If you don't think you got the 2800 deposit from the IRS then Request a trace for a missing third Stimulus payment
https://www.irs.gov/newsroom/questions-and-answers-about-the-third-economic-impact-payment-topic-j-payment-issued-but-lost-stolen-destroyed-or-not-received