Plots adjust the subtitle position

Hi I am trying to plot some subplots with title or label. I tried to use label which was assumed to be appeared within the plot, but it didn’t. Then I tried to use title, it works now, but the position of those subtitle is far from the image. I am wondering how could I adjust the title position and let it close to the image or axis. Thanks. Here is my code and plots:

plot!(plt, contourf!(plt, xs,ys,B[i], subplot=i, title=“z=$(4+i)”, titlefontsize=4, titlefontvalign=:top, showaxis=false, ticks=:none, tickfontsize=4, clims=(-1E+23,0), colorbar_thickness=4, right_margin =, aspect_ratio=float(26/38) ))