Are you asking for help with the process of populating the flowfilter field that you’re creating in user setup, or with the process of applying those filter values to various tables like the Item record? Both maybe?
To give you a quick tip on filling a form control with multiple values from a lookup table (like you’re doing now), take a look at the ClearOnLookup property of the textbox control that you added to the form that you’re using to enter filter values. If you change that value to No, the you should be able to build the filter string you’re describing.