If they had access to your computer they may have installed a key logger or if they have access to your email account it’s easy. All they do is log into your email, then go to any site you have used that email on to register and do a password recovery. They will then get sent the password to that site or a recovery link. Always use a strong password, Letters (upper and lower case) numbers and symbols for each site. Never use the same password on another site.
Register Hereor login if you are already a member