What is the command for dynmap spawn my spawn is at 29000-x , 64-y , 29000-z

dynmap uses the worldspawnpoint, as stated in the component section: https://github.com/webbukkit/dynmap/wiki/Component-Configuration

You may otherwise be wanting to set the world or map 'center'

So do I have to use the command /setspawn or /setworldspawn will that change the spawn point in dynmap like i wanna move that spawn icon to 29k-x 29k-z

Setworldspawn should do it.

K lemme try it