In the Julia REPL, one can delete a method without restarting the REPL by calling Base.delete_method1.
First, find the method:
m = @which fun(x)
where fun(x) will give the method that you want to remove. Then issue:
Base.delete_method(m)
Note that executing workspace() in the REPL will also clear all variables and methods (erasing all work) but without the need to restart the REPL. This is sometimes useful when using the built-in Julia REPL in Visual Studio Code.