In Nokia, I did it by typing
71 for the unanswered calls,
00358 for the Finnish country code and the phonenumber
I know there are many applications for the task but I do not want to use them.
I heard that some Nokia Android phones and Sony phones have a builtin feature for the call forwarding in their phones. However, I cannot find such a feature in my Oneplus.
Phone: Oneplus 3T
OS: Android 7.1.1