Log on to the "Roblox" home page at roblox.com and create a new user account if you haven't already done so. If you don't want to create a new user account, you can also sign in with Facebook by ...

It’s recommended by ROBLOX to send a polite message informing them of who you are and which game you met in, for example, “Hi, it’s me [insert username] from Adopt Me!