A measured, gradual approach.
Start in the first week of life: put a small handful of fresh starter and clean water in front of the calf every day, and remove whatever is left stale. Intake rises to about 0.5 to 1 kg a day by six to eight weeks. The calf can be weaned off milk when it eats about 1 kg of starter a day for three days in a row and is healthy.
Starter is given alongside milk, not instead of it, until weaning. Keep the feed fresh and dry, and clean water always available. If the calf has diarrhoea or stops eating, call a vet.