There are a few ways you can allow your customers to sync their bank accounts in Odoo without giving them complete access to the accounting app.

1. Create a user group with the necessary access rights: You can create a user group with access rights that allow your customers to sync their bank accounts. This will enable them to sync their bank accounts without having full access to the accounting app. You can add your customers to this user group, and they will be able to perform the necessary actions.

2. Use the Multi-user feature: Odoo's multi-user feature allows you to create additional users with specific access rights. You can create a separate user for each customer and give them access to sync their bank accounts. This way, each customer will have their own login credentials and won't be able to access other parts of the accounting app.

3. Use the Portal module: Odoo's Portal module allows you to create a customer portal where your customers can log in and access their data. You can give your customers access to sync their bank accounts through this portal without giving them access to the full accounting app.

4. Use a third-party app: There are several third-party apps available in the Odoo app store that allow you to sync bank accounts. These apps usually have more granular access controls that you can use to give your customers the necessary access without giving them full access to the accounting app.

In summary, there are several ways you can allow your customers to sync their bank accounts in Odoo without giving them complete access to the accounting app. You can create a user group with the necessary access rights, use the multi-user feature, use the Portal module, or use a third-party app.