Well, to stop a sim from being afraid of aliens without having to do any fighting, I'd recommend having your alien sim empathize with their partner, so they can learn that their partner has the Fear of Aliens. When they learn about that, they'll be able to Reassure them about aliens (that should be under the Deep Thoughts category.)
If you want to prevent your human sim from getting abducted again, you can have them Complain About Getting Abducted to their alien partner. Their alien partner will call the UFO to take them off the list.
If your human sim complains and then asks to restart abductions, then they'll be flagged as being abducted voluntarily and will never develop the fear of aliens from being abducted and will always have a happy response and gentle landing. Ask to Restart Abductions is under Interests, after a sim has been removed from the list.
There's also the new Truth-Seeker aspiration, which blocks the Fear of Aliens entirely.
So, a few different ways to do this.