how to use existing wallets by address?

[ddtch]

Hey guys things is next:
in tutorials I see you use code example like:

const mnemonic = "unfold sugar water ..."; // your 24 secret words (replace ... with the rest of the words)
const key = await mnemonicToWalletKey(mnemonic.split(" "));
const wallet = WalletContractV4.create({ publicKey: key.publicKey, workchain: 0 });

and later on refer to the key like:

await walletContract.sendTransfer({
    secretKey: key.secretKey,
...

But what if I do not creating wallet? And I only know the public key and address itself?
For example I use @tonconnect/ui lib to connect wallets of users. Should I use @tonconnect/ui method sendTransaction to acheive same outcome?