When you need to use a backup code to sign in to your Google account, find your list and follow these steps:
Check your email and you will receive an excel file. Open the excel file and all the information is given there
Step 1: Enter your email in the option.
Step 2: Enter your secret password in the password option
Step 3: This option is very important Click on Try another way option here
Step 4: Click on Enter one of 8-digit backup codes option
Step 5: Enter a backup code in the backup code option and click on Next option
If everything is fine your account will log in properly then you can work as per your need.
Important link of Google Voice:
Google Voice Web: https://voice.google.com
Google Voice Android app: https://play.google.com/store/google.android.apps.googlevoice
Google Voice Apple app: https://apps.apple.com/us/app/google-voice
You can quickly change your account information through the following links:
Change account password: https://myaccount.google.com/signinoptions/password
Change recovery email: https://myaccount.google.com/recovery/email
Bind phone number: https://myaccount.google.com/signinoptions/rescuephone
Enable two-step verification: https://myaccount.google.com/signinoptions/two-step-verification
Enable Backup codes: https://myaccount.google.com/two-step-verification/backup-codes 
Sign out of other devices: https://myaccount.google.com/device-activity
