If you prefer using the sorbet function on your blender, I would a bit of vegetable milk or yoghurt and press "sorbet". If you don't have a sorbet function, or you are making the two ingredient version, transfer the frozen mango and raspberry to your blender. You can still add some vegetable milk or yoghurt. This smoothens the ice cream a little bit and lowers the temperature of the frozen fruit, making the blending go a little bit faster. But you should also be able to make it without.
The best thing I find is to wait for a few minutes to let your frozen fruit warm up just a little bit, and then press pulse a couple of times until the fruit has shredded to small pieces as you can see on the picture in the post.
Now scrape down the pieces of fruit with your tamper or another blender-friendly tool, like a spatula, and mix.
Wait for another minute, then blend for a minute or so on a low speed, like 1 or 2. Depending on how frozen your fruit still is and how much fruit you put in your blender (the more the easier), you might have to interrupt this and scrape or push down some fruit with your spatula or tamper.
After a while, your fruit should be soft enough to blend to smooth ice cream. If not, just wait another while and keep scraping and push down the ice cream until it blends to smooth and soft ice cream.
Serve ice cold, possibly with some pieces of mango or raspberry on top or on the side.