I am use my TP account to change the domain name in hands-on org, and I save the domain name, the hands-on org are mistake I am can not log in with my hands-on org anymore
 

I am really stuck. I was having a revision / Salesforce Training day and followed a trailhead instruction to change My Domain. Instead of having a Playfulbear as my linked org I changed the name as instructed. I am now unable to log into it! I try to complete a trailhead challenge and my linked Org is now inaccessible. Please help.