At work, we had need to fix the Pull request purpose to gain in vertuosity and quality of this tool.
The proposed pptx has been partially build on this blog ticket https://runnable.com/blog/the-10-commandments-of-code-reviews
Use it as yours, diffuse it...
PullRequestRules.pptx (8,48 mb)
Last but not least : a good number of approvers should be 2 (small teams) to 3 persons (large teams).