If you haven't added a delivery method 'Click & collect' yet, learn how to do it here.
Go to 'Settings' > 'Payments' > Click on '+ Payment method'.
Add custom name: 'Payment on pickup.'
Change the email template. This message is sent when the order is placed.
Remove the message, for example, about the bank account number and add a few sentences related to the personal pick up of the order.
Finally, choose the type of delivery you want to have for this payment method. You should normally choose the option of personal pickup, click & collect.
If you would like to add payment for download, see this article.