Sorry, mate, but I can’t make myself understand how you can still miss this… :|
In the combat movement phase you must either move your BB or not. If you move it in this phase it is a combat move and you can’t move it in the non-combat movement phase. In this phase you declare all your combats, meaning your BB will have to be assigned to the sea battle. It can NOT be present in the sea battle without participating. Therefore you can’t assign it to do shore bombardment.
If you move it in the non-combat movement phase that is ok, but that also means it can’t conduct bombardment(which is a combat move).
If it is still unclear you will need to be more specific as I feel I’m just repeating myself here… :-)