How can I delete or edit a rule I added to my invoices

Good day, @Cathal_Reynolds,

I want to make sure about the rule you're referring to. Any clarification will help me sort things out.

In the meantime, if you're referring to Bank Rules, follow the steps below to modify them:

1. Go to the Banking menu then select the Rules tab.
2. Find the rule you want to edit.
3. Click the Action drop-down to make changes to the rule.
   

See this link for more information about this: Setup bank rules to categorise online banking transactions in QuickBooks Online 

Also, are you using QuickBooks Online for USA? There are several rulings you can do for this version, namely, Price Rules for customers or the Tags you add to invoices.

While waiting for your confirmation, I'm adding some steps that might work for QBO USA users only.

To edit or delete Price Rules:

1. Tap the Gear ⚙️ icon and choose All Lists.
2. Select Price Rules from the options.
3. On the next page, find the rule you want to modify.
4. Click Edit or use the drop-down beside it to make a rule inactive.
   

Here is an article about Price Rules: Set price rules in QuickBooks Online

To modify tags on invoices, go to the Gear icon choose Tags. Tap the drop-down in the Action column then choose Edit Tag or Delete Tag.

To learn more about this feature, see the following links:

• Tag transactions in QuickBooks Online
• How to use tags?

If you're referring to something else, let me know in the comment below. I'll be right here if you need anything else. Have a good one!