Please follow the below steps to get the LinkedIn App Client Id and Client Secret.
1. First, you need to Go to the LinkedIn Developers' website
2. Once you click the Create App button, the following page will open.
Click the "Create a new LinkedIn Page" and the following page will open :
Click the "Company" link and fill in the following required fields:
After filling out the form click Create Page to submit.
3. Set your app name and enter any additional information required.
4. You will be redirected to the Authentication page where the Authentication Keys (Client ID & Client Secret) and other details will be shown.