3
Chain only runs cleanly when I keep the shifter pressed
(sh.itjust.works)
A place to ask bicycle repair questions, and for bike shop monkeys to share advanced non commercial wrenching resources (no YouTube self promotion). This is only for repair related topics.
Park Tool has some nice videos that take you through the process of adjusting both the front and the rear derailleur. All you need is a screw driver and a few hex keys (possibly).
https://www.youtube.com/watch?v=ZNG7g83lI-s
https://www.youtube.com/watch?v=UkZxPIZ1ngY
Calvin is great at clearly explaining these things, even if they promote their own tools quite a lot. (I am not affiliated with PT.)