Its sad the game doesnt explain all the dungeon related things well to new players so heres a heads up guys - you can literally take off your weapon and still do every dungeon from F8 lobby. All you have to do is go to F8 lobby, select the dungeon you want to enter and instead of clicking LFP which is greyed out you just enter alone. Once you are inside you just click the icon i highlighted in the picture below and voila you can now do any and every dungeon you want.