If you wish to return to Syria, you cannot apply for assisted return. The reason why Norwegian authorities cannot help you with this, is the security situation in Syria.
If you have a permanent residence permit in another country than Syria, you can apply for assisted return through the International Organization for Migration (IOM).
If you have a temporary residence permit in another country than Syria which is valid for at least another 6 months, you can also apply for assisted return. Each application will be assessed individually, and not all applications will be granted.
The IOM can also help you obtain travel documents. If you have handed in your passport to the police, you will get it back at the airport when you are about to travel.
If the IOM cannot help you to return, you can organise your own travel. It is your own responsibility to check if you are allowed to enter the country you wish to travel to.
If you have handed in your passport to the police, you will get it back if you withdraw your asylum application. You will get the passport at the airport when you are about to travel.