magento2.4.1 – How to create Observer for “after save” event in custom module

I am using the custom module, in the backend there are two fields, Field 1 manually entered Field 2 get the values based on Field 1. Here i want to get the Field 1 value in Observer after click save, after getting that Field 1 then i need to pass that value to**SAN**] // SAN is my Field 1 value

The API returns the Location Id which i want to be saved to Field 2