usually for setup time violation you need to reduce the delay of the path leading to the FF D-Input with respect to the Clock .. while for the Hold time, you need to increase the output delay of the Q pin ..
you first can start with what the tool tells you on how to fix timing violations .. then go back to the RTL ..
hi,
basically timing violations will be checked before tapeout. if we have setup violation, you can reduce the frequency and make the chip to work with lesser frequency.
if we have hold violation, the chip will not work. hold violation is important to check during tapeout.