Informal:
* "Só tô vendo se tá tudo bem." (This is a very casual way to say it, common among friends.)
* "Estou só te dando um oi pra ver se tá tudo bem." (This is slightly more formal, but still informal.)
Formal:
* "Estou apenas verificando se está tudo bem." (This is the most formal way to say it.)
* "Gostaria de saber se está tudo bem com você." (This is a more polite way to ask.)
Other options:
* "Tudo bem?" (This is a very simple way to ask if someone is okay.)
* "Como você está?" (This is a more formal way to ask how someone is doing.)
The best way to say it will depend on the specific situation and your relationship with the person you're talking to.