Hello I want to make trigger for If a Territory__c record’s sales representative is changed (and only when it is changed), repeat Requirement #2’s logic for all Accounts associated with the Territory.
Here is requirement 2:
Requirement #2: When an Account’s BillingPostalCode (aka Zip Code), is changed,           
1. Change the Account Owner to the sales representative assigned to the new zip code          
2. Change the Owner field of all the Account’s Contacts to the same sales rep           
3. Change the Owner field of all the Account’s Open Opportunities to the same sales rep