Job's conflict when multiple istances are running

Hi all,
I’m new in Gitlab and I’m using Unreal Engine to make my application, I’m trying to integrate it with Gitlab’s CI but I found a problem. When I have multiple jobs which are running with their own pipeline (e.g. as soon as something has been pushed), there are some cases where a new job starts its pipeline even if the previous job is still running, this obviously makes conflict. My idea is to keep in pending state new jobs while the previous job is still running. Do you have any idea or suggestion on how I can overcome this issue? Thanks in advance.