You cannot send money directly from Apple Pay to Cash App
Add your Apple Cash balance to your bank account
Open Wallet on your iPhone
Tap your Apple Cash card
Tap the More button
Tap Transfer to Bank
Enter the amount and confirm the transfer
Wait for the money to arrive in your bank account
Open Cash App
Tap the Banking tab
Tap Add Cash
Choose the amount
Select your linked bank account
Confirm the transfer
If needed, link the same bank account to both Apple Cash and Cash App