Surely there are a set of Instructions with the set? Of course, the information in there is assuming that you never have a major issue, new or later. And you might not have any issues. And, since the running gear is often carried over to new releases, to find info for a lot of Lionel stuff you have to go to past products' information.
So, go on Lionel's website
( www.lionelsupport.com ) and download the parts diagram and parts list for the 0-8-0 loco:
https://www.lionelsupport.com/...-8-0-1031-Locomotive
The Manual for the Lion Chief (LC) Pennsy Flyer 0-8-0 should work:
https://www.lionelsupport.com/...3984250PAFlyerLC.PDF
We've had the LC Pennsy 0-8-0 Flyer set for two sets of grandchildren for several years. Most of the time you just need to know how to lube (sparingly!), and not overfill the smoke fluid (but don't run it dry either!) Eventually a motor failed, and it was a relatively cheap part (about $18) easily changed out. Probably the problem resulted from hauling around longer trains- the 0-8-0 is best left to pulling 5 or 6 cars (like is in the set).
When the 0-8-0 motor failed (for a later Christmas) I bought a Lion Chief PLUS locomotive for the grandson. Of course, it cost more than a new set, but in my judgement, worth the money.
I took over the 0-8-0, added some resistors so it ran slower, and have that as a switcher on my layout.