I have to install 3 12 channel dimmer panel and all the dimmer panel need an individual 230V-3phase supply, where as in the site only one 3phase supply is available,so please advice as of how to convert this 1 number 3 phase supply in to three numbers 3 phase supply.
The existing incoming power Supply from the main DB is 63A.
Maximum load for a dimmer panel is 40A.

Not sure what type of electrical equipment is existing, seems you would need a 3 phase distribution panelboard, that can contain 3- 3 pole circuit breakers, one for each circuit the dimmer requires.

I have to recommend you call in a qualified electrician to help with getting you the equipment and wiring needed.