Is there any way to automate secrets reading in Gitlab pipeline using service account (add and get)

You shouldn't have to run op add account when using a service account, as the CLI will automatically detect the environment variable OP_SERVICE_ACCOUNT_TOKEN and use that to authenticate. The issue may be that you're not running the beta version of the CLI, which is currently required for service accounts while the feature is in public beta. Could you verify the CLI version that you are using in Gitlab runner? Alternatively, support for service accounts will be included the next production release of the CLI, if you'd prefer to wait for the feature to be out of beta.