How to remove specific pull request from the git branch?

Question

how can I remove a specific PR but keeping local changes and commits in my branch?

these commits and pushes came after the PR that I want to delete.

1. I have development branch, branch 2 that is created from development .

2. I made changes to branch 2 and opened a PR1

3. merged PR1 to development

4. created a new branch from development called branch 3

5. made some changes to branch 3 and pushed changes.

how can I remove PR1(that came from development branch) in branch3?