How can I get access tokens?

You can create a custom app for a store directly in the Shopify admin. To authenticate an admin-created custom app, you or the app user needs to install the app from the Shopify admin to generate API credentials and the necessary API access tokens.

Shopify document: https://shopify.dev/docs/apps/build/authentication-authorization/access-token-types/generate-app-access-tokens-admin