If a receipt scans incorrectly as a cash transaction (the cc number was not clear on the receipt) how can I manually edit this transaction?
If your receipt didn't automatically merge with your credit card transaction then you can manually merge the two by selecting their checkboxes on the Expenses page (via the web) and clicking Merge at the top of the page.
Take a look at How-to: Merge two expenses for an illustrated step-by-step breakdown.
P.S. SmartScan only picks up the merchant name, date, and amount on a receipt, it doesn't pick up card numbers. So you want to make sure that the merchant name, date, and amount are clearly visible on your receipt to make sure that it scans and links up with the card transaction. Deep dive: Troubleshooting expense/receipt merge failures