To position a servo, we need to set up a servo horn so we can see it move, and then plug it into the motor controller board. A servo horn is a small collar with one or more arms, usually used to connect the servo spindle/axle to a mechanism they will move. Your servo motors will come with small bags of hardware, which will contain a few different horn types and screws to attach them both to the servo and the parts you want them to move. The following photo shows the bag and how to attach a horn to a servo:
Screw a one arm horn together with the servo, as shown. Use the very short small screws for this as the longer screws will break the servo. Note that the long collar of the horn fits over the servo's output spindle. Try to line up the arm of the horn in the middle. Importantly, in the last image, don't over-tighten the collar...