Unable to set correct resolution for each monitor

I have 2 monitors that are connected to Dell Dock WD19:

1. Ultrawide Xiaomi Mi Curved Gaming Monitor (DP to DP)
2. Dell IPS P2722H 27" (HDMI port on monitor to DP)

When both are connected, the resolution of ultrawide monitor drops to 1920x1080 (like Dell monitor) and I am unable to increase it.When I disconnect Dell monitor, it works fine 3440x1440. How can I make the ultrawide monitor to work with correct resolution when Dell is connected?