First the solution.

At the intersection in question. Set the directionality of all the incoming roads appropriately.
Highlight the intersection (this will require turning the "Map Problems" layer off).
Use the edit panel "enable all turns" feature.
Put in any turn restrictions that this intersection might have.
Turn on "map probolem" layer and click the refresh button on the layer button.
Note a 6 might be caused by non-connectivity of either end, so fixing one end, might not remove the 6 till the other end is fixed.

Second, a suggestion.
Don't worry about 6's unless they are on a major road, and you have worked every other issue first. 6s, and 7s are the most common errors, and will self correct when someone drives through the area a couple times. Making sure that major roads and highway/freeways work will help out the community a lot more, as this will lower the can't find route, and limit the "weird" instructions normally to the side roads at beginning and end of routes, which again will clean up fairly quickly with a couple drives through the area.

Once all of the roads are connected to the junction in *some* way, click the junction and then click "enable all turns". It's an option on the edit menu.

Another situation that can cause the #6 errors is a one-way dead-end street. Waze sees that you can turn down that road but will flag an error if you can't get back out.

That may also occur on a road that is NOT a dead end if the next segment is set as no entry. The routing basically sees that as a dead end with no way out also.

And of course these things can work their way out with people driving the roads just like the connectivity at the intersection.

I usually don't go looking for #6 errors to fix, but if I am already editing near-by I will usually try to clean at least some of them up.

Excellent answers! Thanks for the info. I will keep in mind that 6's are minor issues. Didn't know they'll work themselves out over time.

I'm getting better at this map editing thing all the time - pretty soon I might just be dangerous at it.