Check what you'd block
Before adding an n-gram as a negative, click its Blocked Search Terms count to see the search terms it would block, and its Blocked Keywords count (Search campaigns) to see your keywords it would affect. You can also tick individual search terms in the panel and add those as negatives instead.
Add negatives
Tick the n-grams you want to block.
Click Add as Negatives in the bar at the bottom.
Check the match type for each. N-grams start as Phrase and search terms as Exact. Use Set Match Types to change them all at once. Microsoft Ads doesn't have broad match negatives.
Choose where to add them: Campaigns, Ad Groups or Negative Lists. Account Level is at the top of the Negative Lists tab. To make a new list, click Create Negative List. You can choose more than one.
Click Add Negative Keywords (the button shows how many).
The negatives are added in your ad account straight away. The n-gram then shows in red in the table, and hovering over it shows when and where you added it.
Every negative you add appears in Change History at the bottom of the page, with who added it and when, and in the ad account's Changelog.