Open Gmail
Select the checkbox at the top left to select all visible emails
Click the “Select all conversations in this search” link if it appears
Click the “Mark as read” icon in the toolbar
To mark all emails in a label as read, open the label first and repeat the steps
To mark all unread emails as read, search for `is:unread`, then select all and mark as read
On mobile, open the Gmail app
Tap the menu icon
Go to the folder or label you want
Select emails manually if needed
Tap the three-dot menu
Tap “Mark as read”