Triple Monitor Setup on Vostro 5490

Hi,

I have the Vostro laptop and I have been using 2 x 27” screens with it via a Lenovo docking station for some time, I have just bought another of the same screens and connected that to the docking station (1 via HDMI and 2 via DisplayPort) when I have all the screens connected only 1 will display in the highest resolution and the other 2 are at 1200 and 800, I’m wondering how I can make them all the same high res as before please