I would then tighten the cooler down in an X pattern, assuring the thermal paste has spread evenly on the contact surfaces, until it feels like the cooler is secure and will not move. If you over tighten you could damage the CPU and/or the socket. If these steps do not fix the ...
Then secure the cooler back to the motherboard using the mounting hardware you just removed to take the cooler off. I would then tighten the cooler down in an X pattern, assuring the thermal paste has spread evenly on the contact surfaces, until it feels like the cooler is secure and ...