You can only close an account on HER from inside the app. You can this by going to: My Profile > Settings > Support > Close Account
When you close your account it will delete all your profile data and you profile will no longer be visible in the meet section of the app.
If you were messaging someone or had posted something to the Feed, that will be visible until the algorithm sorts it out of view.
If you choose to join HER again you will need to create a new account.