It depends on what type of grass and how mature it is. There are several grass-specific herbicides such as Poast Plus, Clethodim, etc. None of them are very effective on grass that’s very mature. So using a grass-specific herbicide depends on the maturity of weeds. You could try mowing but most grass species respond to being cut by growing again if it’s during the growing season.
It may be best to terminate the weeds and crop by herbicide or tillage and plant a fall crop now. If you take this action, make sure there is plenty of soil moisture before you plant the new crop!