what does error code: 0x8019019a mean

Can you clarify? You mention Outlook yet say the problem is with Windows Mail app - which is it?

You change the settings under the Mail app not Outlook.com. If you're using the Outlook email client (not Windows Mail) then you change the settings there.

I suspect that the accounts were set up automatically rather than manually creating them, this is why there's no option to change the password.

If so then you'll have to create the account again.

Yep, I have tried all that before, but I've just tried it again following below:

1. Go to "Tools" in your Outlook client
2. Click "Account Settings"
3. Choose your Yahoo account and click ‘Change’
4. Copy the app password above and paste it into the password field

Gernerate an app password

1. Sign in and go to your Account security page.

2.  Click Generate app password or Manage app passwords.

3. Select your app from the drop down menu and click Generate.
4. Follow the instructions below the password.
5. Click Done.
6. Use this app password and your email address to sign in to your email app

When I went into Yahoo just now, there was this message and I copied it:

We consider security a top priority. We sent an email that we're updating our authentication policies around third-party email access to better protect Yahoo Mail accounts. You may need to update your account settings in third-party programs to use a more secure approach. 

I had no email they mention obviously, But thought it might shed some light on it 

Also, when I am asked to fix theYahoo account I get this message: "Your Yahoo account settings are out of date. Learn more." When I do it says Check Your Password and Check Your Security Certificate, which I've done on both.

Of course it does not solve the Google account where I have no message at all, apart needs fixing with all the email reminders. Anthony

When you change the password are you using the created app specific password or just changing the account password?

Have you tried setting up the account again?

Yes I know the Mail app isn't Outlook, and as I said I have tried endless times to fix those accounts in that Mail app, but they will not stable as ealier times and keep coming back to fix again on both of them. I am having considerable email reminders fom Windows asking me to fix accounts, when I cannot. 

It would be easy any other time, when I would either go in to fix or account settings. The only reason I have changed the password is if it would remedy the situation, as apart from this Ox8019019a code, tells me absolutely nothing as to why, and after spending days over this, I am coming to the end of my tether with Windows and all this security, no matter how safe it makes you. Anthony

I am confused, it is the Windows Mail app that I cannot fix Yahoo & now Google account apps, after re-entering password, and even changing to new passwords. The other accounts are fine & hopefully will stay that way, although I am getting paronoid now. I have reinstalled Office Home and Student 2019, but does not change anything. I've tried to restore the Outlook app to the beginning, but unable, and not sure as informed to check the file history. This app specific password, I've not had before, and unless I am able to in Outlook, how am I going to be able to fix the accounts in the Windows Mail app? Anthony 

The Mail app isn’t Outlook webmail. However it should be easy to fix, on the left-hand side you should see the accounts, if you click on Gmail (or Yahoo to fix that account) there should be an option to change the account settings.

You don’t change the password for the account but the password within the Windows Mail app.