Step 1: there are two things inside the crafting room they will use. One is a filter dispenser, and you will use it to get a Rebreather Filter. You will only be allowed one of these at a time, but after you use it you can get another. Now that you have an Alum Mine Gel Packet and a Rebreather Filter, you can use the work bench right beside the dispenser to combine the items to form an Enhanced Filter.
Step 2: the Enhanced Filters are Tradable... so trade them off to whoever wants to refit their looted rebreathers. NO skills or profession are needed to modify the looted rebreathers with the Enhanced Filters; simply target the workbench and radial it to refit the rebreather. The rebreathers are now also tradeable before or after a refit.