When a player comes to me struggling with a slice, I immediately know that the relationship between their clubface and club path is off. To wit, their clubface is pointing too far right of the direction they’re swinging, which creates too much left-to-right spin and makes direction hard to control.
If this sounds like you, reverse those two things. The next time you’re on the range, place three clubs on the ground: one parallel to your target line for your feet and two forming train tracks pointing to the right of your target (right). Place a ball in the middle of the “train track” clubs and practice swinging in the direction they’re pointing. At first it will feel like you’re swinging out to the right.
This is normal at first — it’ll get more comfortable as you go. Check your divots as you practice and make sure they’re following the same direction as the clubs on either side. That’s your sign that your swing is on the correct “anti-slice” track.