The point slope form is y - y₁ = m(x - x₁)
where m is the slope and (x₁, y₁) is the point.
You stated that the slope is -13 and that the point is (5,7)
Plugging that in, you get:
y - 7 = -13(x - 5)
That is your final answer.
A little note/tip, if you ever want to change from point-slope form to slope-intercept form, all you have to do is solve for y. :)