Hello there, @MySoft.
Thank you for choosing QuickBooks POS as your accounting software. I can share some insights about inventory adjustment.
Currently, importing your data via iif is not an option. You can import and export information in your file using MS Excel. It's imperative you follow the templates and formats to prevent errors when updating or transferring a data file.
If you want to try the available workaround, you can check this article for your guide: Import and Export overview.
I want you to know that your voice matters and I'm submitting feedback on your behalf. I also recommend you sending this request straight to our product engineers. Sharing features and options that you would like implemented is how our engineers look for new product updates. Just go to Help menu and choose Send feedback.
Let me know if you have other inventory or importing questions, MySoft. Please know that I'm just a comment away. Have a blissful day ahead.