Thank you for contacting us. Simple question, but hard to answer without knowing more. What version of mSecure were you using? If previously using mSecure 4, you'll have to download our older app from your purchased list. Here's a guide that can help to learn how to download previously purchased apps: https://support.msecure.com/en/support/solutions/articles/36000064249
Otherwise, if using mSecure 5, just download the app from the App Store and sign in to your mSecure account.
Note that since the older version(s) of mSecure isn't a cloud-based app, there is no way to "sign in" to an account where your information is stored online. Because of this, each older version of the mSecure's login password is device specific and your information is not automatically restored when an older version of mSecure is installed or reinstalled on a mobile device.
Are you running an older version of mSecure on any other devices, and is your data fully intact on at least one of them? If not, have you made any mSecure backups through either the Email Backup feature found in the preferences or through using our free backup software called mBackup? Perhaps you set up iCloud or Dropbox syncing in the older versions of mSecure in the past?
We have an automated reminder in the older iOS app for making backups, so it is possible that you made an email backup some time in the past. Please search in your email accounts to see if you can find an email with "mSecure", "mism" or "mscx" in them. If you find an email backup you can use this guide to restore from an email backup file: https://support.msecure.com/en/support/solutions/articles/36000022240 or in mSecure 5: https://support.msecure.com/support/solutions/articles/36000064291