Change x-axis intervals and labels on cox.zph plot

Hi all,
The plot.cox.zph function automatically plots the x-axis, but I would like
to change the intervals and labels of my cox.zph plots to 0, 50,100,150,
200. However, I cannot get the function to do so. I tried using the
"axis(..." function, but that did not override the existing plot labels.
Below is my code and attached example plots which I am trying to modify.
Thank you in advance for your consideration and assistance.
#plot.cox.zph code
iw.zph=cox.zph(idealweather);
par(mfrow=c(2,1),ann=F,mar=c(3.2,3.5,1.2,0.5),mgp=c(1.7, 0.6,
0),cex.axis=1.1,cex.lab=1.2,cex=0.9,pch=16,family="serif",col.axis=1);
plot.cox.zph(iw.zph);
title(ylab="scaled Schoenfeld",xlab="Time (days)");