I have a prospect who says that they want to come on board with me but that they can’t out of loyalty to their existing advisor. What should I say in my script for this situation?

Ask clarifying and expanding questions in response to their comment and in response to your questions. Go deep. They make talk themselves into working with you.

You may also prefer a more direct approach such as:
- Are you saying that you believe that I am better advisor who you believe would do a better job of helping you get your entire financial house in order and actualize what's on your Financial Road Map?

If the answer is yes, then you might consider giving them a script or some talking points that will help them politely disengage from their existing advisor. It might go something like this, in writing to provide to them to use when they make the call or craft the email to their soon-to-be former advisor:

"We appreciate the work that you have done for us in the past. We have come to the point in our life where we have decided to simplify our financial life. As such, we will be consolidating our financial affairs with one advisor so we can take full advantage of all of our finances being coordinated, comprehensive, and simpler to manage. We appreciate your understanding and support as we make this transition. Again, we assure that this is nothing personal and we appreciate your past service."

On the other hand, if the answer is "no" or "maybe" or some form of hemming and hawing, they may have just been using "loyalty to their existing advisor" as an excuse to not hire you. If that's the case, let them go and continue seeking your next truly Ideal Client.