You need find some information
Go to Manager panel > Storefront > My Themes > Edit theme files
In the left side of theme file manager (tree folder), find file lang/en.json.
Find in lang/en.json with keyword "instagram" near by line 1393, you will see the instagram block.
Change the value of "user_id", "client_id", "access_token" with the information you have get and Save & Apply.