You don’t move the string to contact the front tires. What I did is use fishing strong and a couple of heavy jack stands a couple of feet past each tire. Move the front jack stand sideways until the measurement from front and rear sides of the rear wheel are the same. This establishes a straight line relative to the rear wheels. Now you can adjust the tie rod to bring the front wheel 1/2 the desired toe in. You check this by measuring from front and back of the front wheel to the string. Repeat on the other side.
