Messing with the limit screws when something was working prior and only a cleaning was done is a definite misstep
At that point, I'd agree you need to go back to square one. If this is a Shimano DR then you can find the manuals for your model DR that tell you how to set it up. You need to look for the DM's. The DM for the DR will just give you the installation and initial set up and the DM for the shifter... I think, will have the adjustment procedures..
LBS's don't usually charge much for this if you don't need parts. So if you are just guessing what to adjust, then take it to a shop.