Hi @suyashcyber94 ,
if you are not able to find the config/lighthouse.php file that means installation is not performed properly.

after running the installation commnad :

php artisan bagisto_graphql:install

you can see in the below link ,this will hit to to following file and you can see the publish code for the lighthouse.php file.
https://github.com/bagisto/headless-ecommerce/blob/main/src/Console/Commands/Install.php#L42

so please make sure the installation is properly perfomed.

Also the config folder is on the root of your project.
Thanks!