Your backup file is usually stored in your browser’s cache - this is why whenever you’re logged out, you only need to enter your password to regain access to your wallet. Thus if you switch to a different browser, you have to restore your Guarda wallet before you can use it.
Go to https://guarda.co/app and select Import or Restore, then Restore from Backup. Either drag and drop the .txt file with your backup into the specified field, find it in your files via Browse, or enter the code manually. Then enter your password. Welcome back to Guarda!