The Problem of Adding Functions to array_merge Loop

  ios, question

There is an array

I want the key value of the red box inside to be 0123456789 instead of 0123, 0123 every time.
I want to use array_merge to reorganize, but I don’t know how to write the loop.
Please give us a thought or a new good method.

function merge($prev, $now) {
 return array_merge($prev, $now['item_data']);
 array_reduce($arr, "merge", array());