In QuickBooks Self-Employed (QBSE), changing passwords won't usually affect your invoicing. Since you mentioned being unable to edit and send them, may I know if there's any error you've encountered? This way, we'll be able to know what to do and how to come up with a possible solution for a specific error.
For now, you can use a private browser to rule out any browsing history or cached files causing the problem. Here are the shortcut keys for accessing private browsers: