Get one of these https://www.amazon.com/gp/product/B0821WQJYF/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1
120v 15 amp potentiometer
There are speed controllers for the dewalt, motor control rheostat 20 bucks:
https://www.amazon.com/gp/product/B0821WQJYF/ref=ox_sc_act_title_1?smid=A23J7KC6GONVFY&psc=1