Can I use a single driver to run parallely multiple tests in Selenium (Java)?

With the way my project is structured, it was made with all functions calling one static driver, since I didn't expect I'd need to do many tests simultaneously. Now I'm using TestNG and, right now it's opening up multiple tests and doing both test actions in one of the windows, effectively crashing the test.

This happens because all the basic functions that I've made (such as clickbutton, login user, etc) call a static driver from a class I've named DriverManager. And to change that I'd have to basically refactor the entire code, putting a driver as an entry object to most functions I've made.

Is there any way I can do the tests parallelly using TestNG with only one driver?