Water under the bridge.

Meaning

To imply that a past issue is no longer relevant.

Examples

• John: 'I'm still upset about that argument we had last week.'<br>
• Alice: '<b>Water under the bridge</b>. Let's put it behind us.'
• John: '<b>Water under the bridge</b>. Let's focus on the present.'
• Alice: 'I still feel awkward about that misunderstanding with John.'<br>