You need a good Service & Wi-Fi.
If they are On, turn Off Hotspot & VPN.
Charge the battery > 70%.
See -> If you can't connect or sign in to iCloud
If you can't connect or sign in to iCloud - Apple Support
Have you forgotten your Apple ID?, Check your Apple ID via your email box, see this Apple article: If you forgot your Apple ID
If you forgot your Apple ID email address or phone number - Apple Support
OR see -> Having trouble signing in?
https://iforgot.apple.com/password/verify/appleid
If you've forgotten your Apple ID email address or phone number
If you've forgotten your Apple ID email address or phone number – Apple Support (UK)
Have you forgotten your password? -> 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
Call Apple in your region see: Contact Apple for support and service
Contact Apple for support and service - Apple Support
Contact Apple Support -> Get Support (apple.com)