It’s going to be hard to answer this without being able to see the theme admin. Check to see if there are any theme customisation options in your admin. Some themes may come with their own control panel which lets you toggle settings or alter footer content, like the copyright.
The theme may also have a hook to let you filter and alter the content, again without access to the code I am only guessing here.
A good solution here would be to create a child theme from this, and create a new footer.php template to override the content. Make a copy of the current footer.php and place it in your child theme, and then simply remove the copyright.
Lastly, check the terms and conditions on this theme you have purchased as you may not be allowed to remove the copyright notice.