how to update the Resignation Effective date based on dff field using autocomplete rules

Summary:

Created an Autocomplete rule to modify the Resignation Effective date given by LINE MANAGER/ HR in approval process.

But the effective date is not changing. If we change the Termination Date then Effective date is changing along with that.

But we want to use the custom field in separate section to modify the Termination date in Employee Resignation Flow. which can be controlled by LINE MANAGER/HR

Content (required):

Version (include the version you are using, if applicable):

Code Snippet (add any code snippets that support your topic, if applicable):