Phase 1: Walk your C1 trie. Tap each letter of the pattern bad.
LC 211 — Design Add and Search Words Data Structure

Your C1 trie supports addWord(word) and exact search. Now someone asks: match b.d against [bad, bed, bid, bud, cat]. That . is new. What does it even mean?

First — confirm the trie you built still works

Before the new character appears, walk a plain pattern. Tap b, then a, then d. You are just following one child at each step — the deterministic walk from C1.