how to draw a vertical line from known x axis to kaplan meier curve and from the intersection point to y axis

[Siahrood]

Hi , Is that possible to draw a line from known x-axis pont to Survival graph and from intersection point a line to y-axis in "survival curve based on kaplan meier estimate" ?
I have found by "geom_segment" it is possible but I guess in that case y-axis points are known but in my case y-axis can be define from intersection of the first line with survival graph.

could you please help me in this regard ?
best regards
syahrood