Keep to a routine bathtime, consistent with the person's life-long routine. Never force bathing. If you meet resistance, wait until a suitable time. You may have to lower your expectations about how many times the confused person should have a bath. Have towel, soap, cloths together at the start and show each, so that the confused person can use them in sequence.
Showers usually are more disturbing than baths.
In a plastic bath chair placed in the tub. Next, give a slow, gentle sponge bath while explaining each step. Install grab bars, a nonslip mat, and a shower head on a flexible hose. Keep bathing as private as possible. Allow the confused person to do as much as possible.