I'll bite. How do you reset the AF on a lens??
Fortunately in your case you have the E-620 which does allow you to calibrate the body to a particular lens.
The instructions are in the manual on Page 106/7
Head for Cog I Utilities menu and then to AF Focus Adjust from there.
There is a reasonable explanation
HERE along with a test chart you can download and print out.
It's written for a Nikon, but the same principals apply.
I would actually suggest having the chart appreciably further from the camera if your main interest is birds.
You don't need a chart , focussing on anything at 45 degrees or so should give you a reasonable starting point to begin experimenting, but you need to be clear on exactly what point the camera is choosing for its focus point, hence the black line in the centre of the chart.
Newsprint works quite well if you focus on a black line drawn across it, but ideally you want to have the camera pointing exactly horizontally, focussing on some sort of a test image which is vertical and square to the camera.
If you then have a ruler supported at 45 degrees, it should be easy to read where the focus point actually is Remember you are looking for 1/3 behind 2/3 in front to be in focus, rather than 50-50.
Here's a gizmo I made a while ago featuring a laser pointer to ease setting up.
and as the camera sees it
plus a free one from AP a while ago
From the experience of my home brewed tester, I found the grain on the paper of the ruler more useful than the markings I so lovingly prepared, so the new ruler features some newsprint out of the Guardian.
You don't need anything this fancy at all; I'm just showing it to illustrate the principals. Your camera will remember the serial number of each lens or accessory and support up to 20 combinations with or without teleconverters.
Personally I'd take several photos and determine the most representative out of a batch when you are doing the alterations. It's actually a lot quicker and easier than all this writing would suggest when you've done it a couple of times.
It does need repeating every now and again, I've even found slight variations in the seasons. i.e. freezing cold might need different compensation to mid summer.
Really hunts for focus all the time, which is not what you need when your subject is birds, wildlife and children 
I've looked at some of the calibration software available, but none of them seem to support my camera (Olympus E-620). So anyone have any tips on how to do it myself manually please?
