I'm using an Iframe inside an Iframe and need to change the source for the second one.

This is so when I load a new page I can load the footer and header without pasting them in each different html page. Originally I was using javascript to "add" the code but it only works on/in the replit environment and it's janky.

Example setup

┌────────────────┐
│░░░░░header░░░░░│
│┌──────────────┐│
││┌────────────┐││
│││░░░insert░░░│││
│││░░░░░░░░░░░░│││
│││░░░░░░░░░░░░│││
│││░░░░░░░░░░░░│││
││└────────────┘││
││░░░░footer░░░░││
│└──────────────┘│
└────────────────┘

The header is the main load page, the footer is the footer page and the insert page is the content page (I used insert because of the amount of characters)

So how would one change the insert page source.