Your Micro Mini's dump valves are internal, and the valve handles are connected to a cable that's about 6 feet long, goes from the handles, across between the frame and loops back to the actual valves. They ARE replaceable, but you are going to have to either cut a hole, or pull down the coroplast underbelly. I had my back tank handle jam at a campground, by pulling it out too aggressively till it hit the stop. Bent the soft aluminum rod trying to push it back in. Was able to straighten the rod and gently work the handle back and forth until it freed up. Worried it would happen again, I purchased an external valve that connects to the sewer hose fitting. Sprayed some lube on the rod, and it's worked fine ever since but I carry the external valve just in case. I'm just careful not to yank hard when I open the valve. I did not need to replace my cable/handle, but they are available online, or at Camping world.
Search for: "Valterra 72" Flexible Cable Replacement for Waste Valve Kits" If the rod isn't bent too badly and you can't work it back and forth to get it loose, you'll have to get into the underbelly.
If you contact Winnebego and give them your model number, they should be able to provide you with the proper part number. If not, do some exploratory surgery and verify the cable length. Some people shoot the new cable with cable lube before installing. This may help reduce jams. There's a fitting that goes over the end of the cable that has a place to stick a spray lube straw. Motorcycle stores carry them, and bike repair places might too, as well as cable lube.
Good luck.