If you contribute code to a github project that is no longer maintained

when I was working on a project, I saw a github project that didn"t have any licence information. The maintenance of this project was stopped 5 years ago, and now I want to fix some problems with the code and add some code. Can I directly fork other people"s code and modify it on the basis of other people"s?
because I have never encountered this kind of situation before, I would like to ask you how to deal with this situation. I am afraid that if I handle it improperly, it will cause trouble

Mar.17,2021

fork is finished, just submit it yourself. There is no need to push to the original version. Anyway, he will not maintain it. You are also open source code is not commercial, secondary development is very normal

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