My church ask me to install a sub-panel in the kitchen that they planned to gut and remodle can I go from a existing 200amp sub-panel to another 100amp sub-panel?

Unless you are a licensed electrican or electrical contractor you are not allowed to do this work .

This is a place of gathering !

Get 3 bids from licensed electricians. You may not be able to install a sub panel depending on the existing load. Churches are considered "places of assembly" and the code is very specific as to what can and cannot be done.

Do what professionals do. Calculate the cost of materials, then triple it. Figure out how much time it will take, then double it. Determine what you are worth per hour, then double that. Then call a licensed professional and see how close you are. Then let them do it.