Probably don't need to tune it as much as give it a general service check and clean-up. Should have been winterised anyway if you are in a cold part of the world and the main issue is to flush the fuel system, replace all fuel with fresh, fit the battery (that you have had on a quality maintenance charger all winter of course...) and coat the terminals, grease all points and check the steering and have a good look over the trailer and wheel bearings.
If you want to have a good argument as to what is needed to mothball or re-commission your outboard get a workshop manual. This will instruct in far better detail how to do the above, and show the factory approved methods for storing and servicing your engine.
Unless there is a significant repair like rebuilding the carbies etc. there is not normally any tuning to do - and in these wonderful days of solid state electronics once the timing is set it stays there. The manual stops any arguments and removes any doubt as to the correct procedure. But use a bit of tact when suggesting any change to your step dad - better to give him a copy for a birthday or other excuse than to start telling him he is wrong. Manuals can be found in libraries, second-hand and new on Amazon and at most boat shops.
Good luck.