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Well sure we can help you to remove the popup from your website , could you please share a screenshot with us ? or a website link with us ? , so its help us to trouble shoot the issue
Without know your module of popup and details we cant figure out how to remove your popup. Its not default functionality of magento.
That is coming from Third party extension so you have to check its from your third party extension of site.
You have to find out bm-popup class in your code to check which file contains this class and based on those class you need to figure out for remove popup.
Agree with the suggestion of @Rakesh Jesadiya , Without knowing your module its unable to find exact issue from where this popup is coming out !!
still if you are CSS expert then you can disable this popup by adding below code in your css file :
This will just hide your popup , but better option would be find its module and disable it from there !!