Print lines on waveform

I’m new here and just bought a Nextion Discovery 3.5 display for my project.
It is actually form my espresso machine based on existing project described here. The screen is connected to an Arduino nano 33 IoT.

The idea is to use a waveform to show the generated pressure from the coffee machine in time.
The next step is to controll the pressure, but creating a profile of the desired/configurable pressure during the cofee brew process.

My idea was to draw the this profile on top of the waveform to see how the actual brew process will follow the pre-determined profile.

The issue is that the lines I programmed dissapear when the screen is refreshed. When redrawing the lines (every second) is not very well accespted by the display.

My question is how to draw lines on a pages that do not dissapear on refreshing it.