Dry fit the wall first. The dollhouse assembly process does not take into consideration finishes so what might work well for an unfinished dollhouse, will not for one that already has finishes applied. For this reason, you might need to cut off tabs from this wall so it will slide in easier and not damage any finishes. Sand the slot well, with a nail file, so there are no splinters that can snag the wall as its sliding into place. Sanding the slot will also make it wider for an easier fit.
Do not apply glue to the wall until it's in place. This will prevent glue from dripping and damaging finishes. It will take a while for this wall to go in so glue will just get in the way and drip out of place. Once this wall is through the porch roof slot, it's not going anywhere.
Use a rubber mallet to help the wall slide down. Be firm but gentle since you don't want to break anything. If something does break, it can be easily fixed. It's just wood.
Once the wall is in place, you can apply glue to the edges and clamp it with masking tape.
