How to plot a constant line, a calculated value from prometheus


I have one graph with two time series imported from a promql.
I can plot and all works well

Now, I have an scalar value calculated from prometheus. I want to plot this value for all visualized time series.

The problem is that I can see the value as instant and table, but I don’t know how to plot for all the time?
Need to do a transformation ?
Is possible to achieve this?

(This is about a network interface bits in/out transit, the straight line is a percentile95th but all is calculated from Prometheus)

Many thans for advanced