First thing to check is if your GPU supports Displayport 1.2. Because anything lower will not allow multi-stream at all.
If it does, you have two options:
One of your displays supports daisy chaining, so it has an output port that you can connect to your 2nd display. The last monitor in the chain doesn’t actually have support dasiy chaining.
You buy a MST hub, which is an adapter that connects to your display port and turns it into multiple displayports to which you can then connect your displays individually. In this versions none of the displays have to support displayport 1.2 just your GPU.