Airline or air miles co-branded credit cards will automatically transfer the earned miles into your air miles account. For other credit cards, you need to transfer reward points into air miles yourself via e-banking or by calling the customer service hotline. Some credit cards may set an expiry date for reward points from 1-5 years (usually 2-3 years). But there are a few credit cards that have no expiry date on the points, such as DBS Black World Mastercard and American Express credit cards, giving you more time on earning points for flight tickets.
Air miles have their own expiry date as well. For Asia Miles, redeemed miles in the account will no longer expire from 1 January 2020, as long as you earn or use the miles at least once every 18 months. Avios has a similar rule which expires after 36 months in an account with no activity.