See -> If you can't connect or sign in to iCloud
If you can't connect or sign in to iCloud - Apple Support
See this Apple article: If you forgot your Apple ID password
If you forgot your Apple ID password - Apple Support
Then see this Apple article: What to do after you change your Apple ID or password
What to do after you change your Apple ID or password - Apple Support
B T W:
You are sign in here . . . with your Apple ID & Password.
Your Apple ID is the personal account you use with all Apple products and services. It includes the email address and password you use to sign in, as well as the contact, payment, and security details that you use with Apple.
You can’t merge multiple Apple ID accounts.
What happens when you use the same Apple ID & Password that you use to sign in here?
See the following Apple articles
Sign in with your Apple ID -> Sign in with your Apple ID - Apple Support
Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)
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See this Apple article: If you forgot the answers to your Apple ID security questions
If you forgot the answers to your Apple ID security questions - Apple Support
👉Scroll to Reset your security questions
- Go to iforgot.apple.com.
- Enter your Apple ID, then select Continue.
- Choose the option to reset your security questions, then select Continue.
- Enter your Apple ID password, then select Continue.
- Follow the onscreen steps to verify your identity. The information you’re asked to provide may vary based on your account details and other factors. If you don't get any options to verify your identity, you can't reset your security questions at this time.
- Choose new security questions and answers and select Continue. See our tips for choosing security questions and keeping your account secure.
After you reset your security questions, you might want to set up two-factor authentication instead. It's the best way to keep your account secure, and you won't need to remember any security questions. You can set up two-factor authentication right from your iPhone, iPad, or iPod touch with iOS 9 or later or your Mac with OS X El Capitan or later.
If you answer your security questions incorrectly too many times in a row, you temporarily can't use your security questions. Try to reset your questions after the waiting period ends.
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Get support and assistance from Apple directly, see -> Contact Apple for help with Apple ID account security
Contact Apple for support and service - Apple Support