This is what we call "Installer support". In order to allow the KNX professional that manages your Thinka access, go to your Thinka's web interface and then to Settings -> Smart Support.
Then start it and use the Copy URL and share this link with your installer via e-mail, whatsapp or any other way that you trust.
With the link (URL) your installer has access to the web interface of your Thinka. If you have a password set on your Thinka, either remove it (see here) or share it too.
Be careful with sharing this URL and password, anyone that gets hold of it, can access your Thinka's web interface.
You can always decide to revoke the access again. After 14 days we automatically revoke access to protect you from forgetting to revoke it all together. The next time you grant access the URL will be different.