The easiest way I find to do it is to replace the extract with enough base grain to give you the OG (based on your setup’s efficiency). The specialty steeping grains would just be added to the mash. The type of base grain to use should be based on the type of extract that is used in the extract recipe. “light DME” can usually safely be replaced with 2-row.
Most extracts have a corresponding base malt they are made with. It gets a little trickier when the recipe has things like dark malt or amber malt. It’s not always easy to find what base malt/specialty malt was used to create that extract.
All that aside, I personally think its just easier to just look at some well known recipes for the style you are brewing and copy that grain bill. It’s much easier than trying to convert in most cases.