I have no health concerns other than being completely detrained on the bike, where should I start?
Why do you think you are "detrained"? Since you posted in a training forum - what are you supposed to be training for?
I suggest you ride your bicycle several times and make note of how you feel when you finish. (anything hurt?}
Then - I suggest you measure your ability using equipment and a course that you plan to "un-detrain" with.
Good luck.