Hi @jibran and welcome to the community.
It’s unfortunate you’re not able to attach files yet but this documentation might help you with this lookup values function here - XLSForm Docs
On first glance it looks like you’ve left out single quotation marks to make it 'reg_ben2'
Secondly, you might also need to specify the filter expression in this case. This syntax from the shared docs should be able to get you going
instance('list_name')/root/item[filter expression]/desired_property
So let’s assume you want to pick a province based on the country that means your syntax will look like so:
`instance(‘reg_ben2’)/root/item[filter expression]/desired_property
Additionally, if this sheet is dynamic and linked to another Kobo Form you can check out this article - Dynamic Data Attachments — KoboToolbox documentation
