How do you help someone who’s isolating themselves?

I don't wanna help those people. Maybe they need that for a bit

You can try to convince them how unhealthy it is to isolate one's self from everyone, but in the end they have to want it.

Try being there, but not engaging in conversation or anything.

When I literally stayed in bed not doing anything for days when we lost our son, my husband just sat in the same room with me, that helped me come back from how numb I was. It helped.

I'll just let them know I will be there when they have had enough of isolation.
I'll maybe ask them how they are time to time. Just to remind them I am there thinking of them.

Sometimes a little isolation every once in a while can be good, however make sure they know you are there for them if and when they feel like reaching out. Try to keep communication flowing and you can try to talk them into maybe meeting up somewhere or even just going for a simple walk or drive around town.

Let them know you're aware of it...
Let them know you're there for them...
Let them resolve the issue as [b][i]they[/i][/b] see fit.

Encourage them to go out and /or visit them if they're up to it