Hi, you can actually try to solder it. You of course have to be careful with the foam. Try to lift the wires from the foam a little bit. Should be enough to protect the foam. Otherwise just put some thick paper inbetween. The wire itself is a coated copper wire. While soldering the lacquer/varnish is removed by the heat of the soldering iron. This is great because it is need to actually make a stable contact.
Let me know if it worked. Ulrich

Hi, just trim the tail a little bit. Right now the plane tries to climb a little bit too much. Just bend the whole tail a little bit downwards for a few seconds. I general you can trim the plane for high/low speed with the tail. Just try it upwards and downwards to learn about the flight physics. :-)