Not able to access my Verizon account

Hello all, 

I can no longer access my Verizon Internet account.  I am using Thunderbird to access my emails and need to configure my Verizon Yahoo account to "Allow apps that use less secure sign-in". This will allow me to use Thunderbird. 

However, every time I attempt to access my accoung via "" or 

"login.", I'm asked to use my VALID password. When I attempt to do so, I'm sent around in a loop and cannot access my account. I contacted Verizon Yahoo and they were not able to solve the problem. At one time I was able to access my account and make these type of changes. 

I've gone repeatedly on the Verizon website and there is no help for this issue and no phone number to call. The "virtual agent" is poor and cannot help. 

How can I get into my Verizon Yahoo account to make SPECIFIC changes other than password, etc?

Thanks for your help.