After a long travel in New Zealeand I ended up with having about 5000 USD (selling my car/transport on very last day I was there).
Whats the best way to get those converted over ? I tried going to my bank (PostFinance) but they would only accept USD and Euro.
Any recommendations ?
You got that in cash?
If not then Revolut, otherwise no idea other than regular exchange offices.
Yeah. Cash.
Tried getting my back to just transfer the value to revolut IBAN but no luck 
Find someone who goes to new zealand and needs cash and exchange in person - try asking at work or some big forums
Big banks (UBS & co) might exchange it for you but will take a few percent cut to deal with the cash. And specialized currency exchange kiosks take >5-10% cut
You can maybe negotiate with small currency exchange shops.
Coop Depositenkasse had the best rates when I checked. You may find some hints here: