How do you activate the members card in Pokemon?

You can't activate a "members card" in Pokémon in the way you might think. There isn't a physical or digital card system in Pokémon games that you need to activate.

It's likely you're thinking of something else. To help me understand what you mean, please tell me:

* Which Pokémon game are you playing? (e.g. Pokémon Scarlet/Violet, Pokémon GO, Pokémon Trading Card Game Online, etc.)

* What specifically do you want to activate? Are you trying to access a feature or unlock something?

Once I have more information, I can help you!