How do I sign in to my secondary Apple Account?

"how i can make my second icloud account as primary account without logging out from old one, because old account is locked?"

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Using Another Apple ID Simultaneously on a Device:

You Can't. You can only have one iCloud Account signed at a time to a device. If you want to access this data, then you can use Family Sharing. Go Here: If you Forgot your Apple Account Password - Apple Support

So, Contact Apple Support.

Unlocking Your Locked Apple Account:

Observing your post, it appears that you are unable to access your Apple Account, being that it has become locked. So, if that is the case, here is the information to use:

See if this Helps: If your Apple ID is Locked or Disabled - Apple Support

If that is of no success, then give Apple a Direct Call:

As you might suspect, no one here would know the reason for the occurrence, of course. So, contact Apple. They’ll know why this occurred and will run you right through how to fix.

Contacting Apple:

• Contact Us - Choose Locations
• Proceed from there as necessary
• Note: Phone calls are taking a bit to go through at the moment, due do lots of calls. With the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple. So, just stay on the line, and you will get through :)

For Note:

There are quite a few reasons as to why this may have occurred. Some possible reasons include:

• Too many unsuccessful login attempts
• VPN (Virtual Private Network) usage
• Disobeying Terms & Conditions
• Consistent transactions
• Session Times Out

"Yeah, but im trying to make my secondary icloud as primary one, but how can i do that without sign out my old one? Is this possible? Because i tried everything and its not working? What about if i reset my phone? My old account its locked. Seems no way i can unlock it."

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No. You need to unlock your account. It's a matter of Security & Privacy. Just think about it: If you were to change the Apple Account, then anyone could change it.

"How do I sign in to my secondary Apple Account?: How I'll unlock it? It says now, account is locked, it can not be used. How I'll do it now.?"

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Recover Using a Computer:

Using a computer, start account recovery from iforgot.apple.com through your device’s browser. Use a computer, as it would be more user-friendly doing so.

Wait it Out or Contact Apple Support:

So, why is it locked? If Apple locked it on you due to too many incorrect login attempts, then wait out the time shown. You can also contact Apple Support, and ask them why this occurred. See my original reply.