If your account is on a workspace that has the signed-in devices feature, the account Settings page has a card called Where you're signed in. It lists the browsers and phone apps signed in to your Rosterr account, so you can end any you do not recognise.
This feature is rolled out in stages. If you do not see the card yet, it has not been switched on for your account's workspace. Signing out on a device always works.
What the list shows
For each sign-in: the kind of device (a browser or the phone app), roughly when it was last used, and which one you are on right now.
End one sign-in
Choose End next to a device. That device is signed out the next time it contacts Rosterr (within seconds). It will need to sign in again.
Sign out everywhere else
Choose Sign out everywhere else to end every sign-in except the one you are using. Use this if you lost a phone, used a shared computer, or think someone else has access.
Good to know
Each sign-in is noted at most about every ten minutes, so "last used" is approximate.
Ending a sign-in does not delete anything. It only removes that device's access.
If you also want to stop a phone getting pings, signing out of the phone app removes its notification registration automatically.
Changing your Discord or Roblox password does not end Rosterr sign-ins by itself. Use this list.
Related articles
Sign in with Discord and Roblox (and link both accounts)
Why can't I sign in or see my workspace?
Notifications and pings: the bell, phone alerts and what you can switch off