I am always happy to provide advice and sometimes I can provide examples if I have enough free time.
But what you are asking has nothing to do with the inventory system at all and there is plenty of information on editing UI’s in unreal using UMG.
Basic problems like this help you learn and get familiar with game development in unreal. The more you learn the easier it will be to understand and start making complex changes.
There are always plenty of results if you google ue4 + your topic. Answer hub always has lots of people asking a lot of the same things.
Down near the bottom of that post you will see how you can get the mouse position and set the widget to that location. You will need to take into account your screen resolution and UI scaling if you are offsetting it.