When you go up to a piglin, the open button appears on the bottom.

Thank you for your report!
We're actually already tracking this issue at MCPE-79376, so I will resolve and link this ticket as a duplicate.

If you would like to add a vote and any extra information to the main ticket it would be appreciated.

If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.

Quick Links:
📓 Issue Guidelines – 💬 Community Support – 📧 Customer Support – ✍️ Feedback and Suggestions – 📖 Game Wiki