Sending zaps is similarily as easy as receiving them;
Best way is with NWC (Nostr Wallet Connect)
Many apps support it, and it makes zapping pretty seamless. Check it out here👇
More flexible but bit manual way
- Tap the ⚡ icon on the note you want to zap (if your client has that)
- you should be prompted to select which lightning wallet on your phone you want to open
- select app (say Wallet Of Satoshi), and it'll copy/paste the invoice for you automatically
- click "confirm" with the amount you want to send
Your zap has been sent
Which device are you using? iPhone or Android? Android has more flexibility