If the ski boot has removable heels, replace them by unscrewing the heel piece from the ski boot and exchange with a new heel. Replacement heels often come with a toe piece or are just one unit and are available at ski shops and from online retailers.
Replaceable toe and heel sets are a new feature offered by ski boot manufacturers such as Lange and Alpina. Walking in ski boots wears down the heel and toe and makes the boot unsafe to use in bindings because it affects the release. Heel protectors are available for walking on hard surfaces in your ski boots. Walk as little as possible in ski boots to save on wear and tear. Have your shoes available for walking any distances.
Unfortunately, if the ski boots do not have replaceable heels, the entire boot, or at least the shell, has to be replaced if there is wear. Have boots tested in the ski-mounted bindings to be used to confirm that the release function is operating safely.
To obtain replacement heel parts, contact the location the boots were purchased, another ski shop, the manufacturer or a third-party retailer. Many shops do the heel replacement free of charge with the purchase of the parts. Purchase extra heel and toe sets in case the model's availability is limited in the future.