Your previous employer was required to mail your W-2 or make that information available to you online no later than January 31, 2019, unless an extension had been filed. Are you able to call your previous employer and verify that it has been sent out or made available electronically?
If they say it has been sent out and you haven't received it, or you otherwise can't gain access to your W-2 online, I would first double-check the address on file with them and ask them to issue you another one.
