There is a manual https://docs.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue and I cannot complete the 4th step because I cannot find "Linked issues".

There is a manual https://docs.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue and I cannot complete the 4th step because I cannot find "Linked issues".

just write #issue number in pull request description to link the isuue
you can also write fixes #issue number closes #issue number to automatically close an issue when your pull request is accepted and merged
if you are the owner of the repository you can link an issue by clicking the setting icon in the Linked Issues on the right sidebar but if you are an outside contributor then you cant use it to change or link any issue you can only see which issues are linked