i already did but i can only generate the instagram test token for the instagram accounts i own and they are in my meta account overview. I will do it for my client instagram account - do i need the access to his main meta account?

https://developers.facebook.com/docs/instagram-basic-display-api/overview

when i click on the button to create the user token (user token generator) i can only see my personal instagram account. how can i log in to the external account to verifiy it?

If you don’t want to read docs, hire a developer

i only want to do this: https://academy.bricksbuilder.io/article/instagram-access-token/

Like I said, if you don't want to read the docs and/or are no developer, hire a developer