Where I can find any guide or thread about it?Import via icloud csv or vcard or use mac contacts app + icloud
Where I can find any guide or thread about it?A pretty well known method is using a .vcf file with a list of contacts and importing it via the Files app or iCloud. If you’re using a jailbroken device you could also go through tweaks like Filza + manual database edits or using My Contacts Backup + sideloaded vCards can work too.
Once imported allow IG to sync contacts.