Here are the following steps that I used to transfer my contacts from my Galaxy S6 to my iPhone 7 :
1. Go to contact and export your address book to the android device
2. Connect your phone to your computer and copy the .vcf file on it
3. Create a new e-mail and send the e-mail to the address that it is configured on your iPhone device
4. Attach the .vcf file and send the e-mail
5. Go to your iPhone and look for that e-mail
6. Once you found it, open the attachment and upload the contact to your address book
That is all.