Slots on the Pokepedia trainer card are filled by clicking the slot itself, not by a sidebar control. The picker modal searches the full 1025-Pokemon roster.
Step 1
Click an empty slot. The slot reads Empty until a Pokemon is set, then shows the sprite.
Step 2
The picker modal opens. Type a name or a Pokedex number in the search field at the top, and the grid below filters down to 40 matches.
Step 3
Click a Pokemon to place it in the slot. The sprite renders on the card and the modal now shows Nickname, Lv, and Shiny controls for editing.
Step 4
Close the modal with Done, the x in the top right, or the Escape key. The Slots +/- counter in the compact strip under the card adjusts how many slots are on the card, from 1 up to 24.