How do I choose a weekly trait in order to host a party?

How do I choose a trait in order that my Sim can host a party?  

One of my quests is to host a party in my home, but when I click on to throw a party I’m receiving an error message saying my Sim hasn’t chosen his trait yet this week. 

When I go to my heirlooms to choose a trait there are no instructions on how to do that. When I tap on one it wants to charge me 5 tickets just to trade it out with something else. Is that what it means when they are asking me to choose a trait for the week?  How do I choose a weekly trait?

i also have another question regarding events with an elder. I just retired a Sim, but I have no idea how I participate in a family event with him. When I click on him it only allows me to build a friendship with him. How do I do an event with my retired Sim?

honestly, after playing FreePlay for 4 years straight this new Mobile version is very confusing.