Hi there and welcome
Can you tell me please exactly what it is you have lost?
Is it emails from your account?
Please let me know
Do you still see any of your emails at all listed there?
ok, it looks like you are signed into the wrong account, in Gmail click on your initial in the top right, in the circle, then click on Sign out.
Then choose Sign in, Sign in with another account and make sure to enter in the correct information for your sign in.
Once done you should again see your emails
Let me know how you go