Micro-Service is about having many projects on git within different repositories.
So, what is the best way to manage an issue, when there is a bug which needed to fix the code on multiple services?
In short: You have to open specific issues/bugs on each repository regarding the specific shortcomings of the service in the repository. The microservices architectural style is all about loose coupling, so an issue should in general be local and treated as such. It is expected that a service is owned by a dedicated team that will be able to fix the specific issue in their service, but nothing in other teams services anyway.
If in your specific architecture it happens often that you find yourself fixing a single issue in many services you probably have to rethink the service boundaries because they may not be as loosely coupled as desirable. Note that finding the right service boundaries is probably the hardest problem when applying the microservices architectural style.
Here is a further read.