How to Change Letter Head in Sales Invoice

I want to have 2 different letter head. One for Purchase Order and Other for Sales Invoice.
I have created 2 letter heads.
How do I assign each to their respective doc type

Just create two different custom print formats for each doctype: Purchase Order and Sales Invoice. Each one with its letterhead format.

In the Printing Settings section, you can set the Letter Head. You can Customize and set the specific Letter Head’s name as Default in that doctype

I tried, but its not happening. Can someone share a screenshot or video ?
Many Thanks !

i think there is no any setting available for use auto 2 different letter head for same company. you can add this script in custom script.

frappe.ui.form.on(cur_frm.doctype, {
onload: function(frm,cdt,cdn) {
	if(frm.doc.__islocal){
	if(!frm.doc.letter_head){
			frappe.model.set_value(cdt,cdn,"letter_head","Surat")
	}
	}

    }
});

Here “Surat” is my letter head name so you should change it by your letter head name. you want in purchase order and sales invoice so put this script for both purchase order and sales invoice.

Same for Sales Invoice :-

Is this setting still exit?

Yes, you can still do this. Also, if you want a particular print format to be default for that document type, go to Print Format list, select the print format and check the “Make Default” button.

This way, you don’t need to select it at individual transaction level.

Hope this helps.