How do I know login and password of my virtual machine

I use a virtual machine called 'RelaxEd' on VirtualBox (Ubuntu 16.04 amd64). After starting it I will be able to access localhost:3000 and then load the web pages. For some reasons I copied its files from Virtualbox VMs folder to another computer (still Ubuntu 16.04 amd64) in order to use it on that second computer. But when I start the virtual machine I'm asked login and password which I don't know. However,it isn't required in my first computer ( I guess login and password were saved). I also created a snapshot of the VM in the first computer and copied it to the second PC thinking I would be able to use without login and password. But I can't start the VM on the second computer by that snapshot either (after loading 90% an error is appearing). How can I get the login and password of the VM to use it on the second computer?