Unable to connect to your account - Gmail migration issue

Unable to connect to your account - Gmail migration issue

Hi there, 

A new user today :) Am trying to migrate emails from my Gmail account to my new domain name business account but receive the error above. A search of old topics shows you need allow access from less secure apps in your google account, however, this is no longer an option in google since this year. 
So, how do I resolve it, please?
Much appreciated :)