Check the grip
Before you change anything in your swing, look at your grip. A grip that is too weak (hands rotated toward the target) makes it very hard to square the face (point it straight at the target) in time. Strengthening it slightly is often the fastest way to reduce a slice.
Make the change, hit a small bucket focused only on that, then retest. If your report named a different cause, follow the report — this is the common starting point, not a universal answer.