You can find other solutions by specifying the intial guess for other solutions. In your case, you can graph the LHS and RHS your equation,
eq1 = 2*cot(x*top/bottom) == tan(theta0);
to find out the intersecting points and specify the initial guess around those values where the graphs of LHS and RHS intersect each other.
Please refer to the example in the documentation where it is shown for the multiple solutions for the below equation:
eqnLeft = 200*sin(x);
eqnRight = x^3 - 1;
title([texlabel(eqnLeft) ' = ' texlabel(eqnRight)])
Hope it helps!