Hi @minhtran91,
Only Klarna can configure a Klarna merchant id to change the payment methods for that merchant id. Each payment method should work the same though for the Woo integration, so there should not be a need to test each payment option in a dev store.
To test in development mode, you can easily get Klarna test credentials with limited payment methods at: https://developers.klarna.com/documentation/testing-environment/
Also these other test stores are available that might be helpful to see the flow across different regions and payment options:
Woo: https://demo.krokedil.se/klarnapayments/
Klarna: https://www.klarna.com/demo/
If you need further support regarding Klarna payment methods, please contact Klarna merchant support per: https://docs.krokedil.com/article/304-klarna-contact-merchant-support