To set a unique link to your quiz, you need to start editing your quiz and then open the “Embedding” tab.
Next, in the “Direct link to the quiz” block, select the link type: Standard or Subdomain:

Fill in the “Unique link” field and click on “Publish".

P.S. The link must contain from 4 to 20 characters inclusive. It can contain Latin letters, numbers, and special characters. A dash “-” and underscore “_” are allowed.

Done! You can open your quiz using the unique link which looks like this: https://mrqz.to/unique_link
or this:
https://unique_link.mrqz.to