If you have a paid subscription:

• Open the Grid tab → Add a new empty post to the feed;
• Tap the Select button → Select a new post in the feed → Tap ‘Pin.’
• Open the Instagram app → Copy the IGTV / REELS post’s link.
• Open Content Office → Tap ‘Paste’.

If you have a free subscription:

• Open the Grid tab → Add a cover photo of your Reels post
• Tap the Select button → Select this post in the feed → Tap ‘Pin’;
• Select the date when your Reels post was published → Save;

If you can't Pin IGTV / Reels posts, please check if your Instagram account is connected to the Safari browser. Open instagram.com in Safari and sign out. Next, try to Pin a post again.