How to change wallet to testnet instead of mainnet

Why do we need to change to testnet?

Before a dapp launches on Cardano, it will initially launch on the Cardano testnet. This is used to test the functionality of the smart contracts used. Tokens have no monetary value here so if bugs are found, no user funds are lost.

Nami Wallet

Eternl Wallet

Flint Wallet

CardWallet