Configure Start

Flow: Record - Triggered Flow

It will trigger the flow when Account object is update and one of the following fields is changed.

• Billing City
• Billing Country
• Billing State
• Billing Zip/Postal Code
• Billing State

Get Records

Get all the existing records from Contact object which has a relation to the Account record.

Decision

Create a decision to check if there is any related contact or not: 

Loop

Start a loop which will iterate the items of the collection you created with the name "Get Existing Contacts":

Assignment

Assign all the fields of the loop which you want to update to the fields of the Account:

Note: The current updated account is available as $Record and $Record_Prior

$Record has the new (updated) vales of the fields.

$Record_Prior has the prior (old) values of the fields. 

New Resource: Variable

Create new resource:

API Name: GetAllContacts

Date Type: Record

Allow multiple values: Selected

Object: Contact

Assignment

Create another assignment the store all the updated records iterated from loop in the new variable.

Update Records

Now, it is time to update all the related contacts (if any).