hello and welcome to the forums

to create a julia image out of a working mandelbrot, it is really mindblowing easy,
exchange the "c" value with your "start" value!
e.g. you did for mandelbrot
z0=(0,0) <<- pixel pertubate
z_n=z^2+c <- seed ( usually the pixel )
in julia mode you do:
z0=c
z_n=z^2+(0,0) <- previous pertubate, now seed
for (0,0) you get a circle shape because you are just squaring a location ... which will bailout instantly....