I used to be in a relationship with an 385 INTJ who just isn't successful in many areas of life if I had to phrase it nicely.
Two routes to go about it:
A) Reassure them that there is such a thing as successful failures and that winning and succeeding are not inherently synonymous. Chances are, they're bitter and more mad at themselves than the world around them, so it's important to clarify to them that it's not the end of the world and that they don't have to do anything. No one thinks lesser of them because they aren't winning 24/7 and it's won't do anyone any good if they keep going on thinking that way. Essentially, let them know it's okay.
B) Support them by giving them the tools needed to succeed if they can't do so on their own. Not necessarily saying to coddle them or do the work for them (they probably wouldn't let you anyways), but encourage them and assist in the problem solving process. If they recently lost a competition, help them identify what could be done better next time, and then if they want you to, join them in the attempts to self improve. If it's one of those middle of the day "Oh god, I'm a nobody with a dead end life" fits 3s can throw, remind them that everything takes time and suggest ways they can more actively start moving up in the world. Usually it'll be something as simple as exercise or take a class on something and that should at the very least keep them busy.
Whatever you do, don't lie to them. Flattery is easily the worst way to help them when they're like this. If they fail to realize you're lying, it'll encourage them to stay in a negative whiny place and if they do recognize that you're just trying to make them feel better, it'll really hurt their feelings. Regardless of wing or variant, it's better in the long run to dish out tough love when you see an unsuccessful 3 be unsuccessful.