Step 1:

First of all go to https://www.instagram.com/developer/ and login/register to Instagram.

Step 2:

After login click on Manage Clients, and then click on Register a New Client.
step-2

Step 3:

Add your Application Name,Description,Company Name,Website URL,Valid redirect URIs (See your Redirect URI in plugin setting page.), Privacy Policy URL, Contact email
step-3

Step 4:

Get your Client ID and Client Secret. and put into the plugin setting page.
step-4