How to Reactivate Yahoo Mail Account 

Yahoo may have terminated your email account if you requested that it be erased, if it remained dormant for more than six months, or if you violated Yahoo's Terms of Service. You can recover and Reactivate Yahoo Mail Account  if it was removed within the last 90 days and wasn't deactivated because you violated the Yahoo Terms of Service.

Follow the below steps

1- Go to Yahoo's home page and click Sign In.

2- After that, input your Yahoo email address and click Next.

3- If your account can be recovered, a selection will appear. Choose a method of verification. Send a text or send an email.

4- Once you've decided on a recovery technique, you'll be given a code. Enter the code that was sent to you in the mail.

5- If you input the correct code, you will be prompted to create a new password. To create a new password, select Continue.

6- Tap Continue one more time, and you'll be asked to confirm your account recovery options.

7- To amend something, touch on the pencil symbol, or to add accounts, pick Add email or mobile number. Otherwise, choose Looks nice to proceed.

8- Your account has now been successfully recovered and is ready to use.

Source:   https://morioh.com/p/9da2a034bce5