How can i access the exact amount for advance child tax credit?

You can check your bank account if all of the payments went to that account.   You should have letter 6419 from the IRS that shows the amount of advance child tax credit payments you received from July to December.   The amount you enter needs to match that letter.  If you are filing a joint return you should both have that letter.  Another place to check is your online IRS account.

https://www.irs.gov/payments/your-online-account

Federal>Deductions and Credits>You and Your Family>Child Tax Credit

The IRS is sending out letter 6419 to you.  It will show the amount of advance child tax credit that you received during 2021.  Enter the information from that letter carefully.   

The remaining amount of CTC that you can receive will show up on line 28 of your 2021 Form 1040.   Then it will calculate down to the refund you see on line 35a or the tax due on line 37.

PREVIEW 1040

https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing

Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.

NOTE:   The CTC is indeed a “credit” that can be applied toward any tax liability that you would otherwise have to pay as “tax due”  to the IR