SEKONDA: HOW DO YOU REPLACE THE SNAP ON BACK COVER?

Sorry, but your hands (especialy fingers) aren't strong enough. Nothing personal- just confirming the fact. My hands can handle 50 ATM casebacks, but I would say this is more expierence than strength.
OK, back to business: align the winder groove first and make sure this side of caseback sits in properly in case. Then use your thumbs to push the opposite side of caseback in, supporting the watch by your palms and knees. Do not try to push the caseback in bit by bit going all around the caseback. This sort of action will never work.
So, align the groove, support your palms by the knee(s) and push the opposite (to the groove) side of the caseback in to the watch case by one, but strong attempt with your thumbs. It should snap in.
If this doesn't work, you will need to ask the watchmaker to close the watch.
NB: Watchmakers are using specialized press for closing watch cases wich do not require any strength at all.

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My wife's waterproof to 100 ATM Anne Klein II watch
had this problem. I got my small metal 1-1/2" jaws screw type vise. (Entire vise is 3" long by 2" wide).
I wrapped a penny 3 o4 4 times around wit a strip of tissue to place over the crystal and placed a dime over the back, then screwed the vise slowly until the back popped in. It ewas easy to tell when the back popped in because it created a bit of slack oin the vise.

Hi My wife has a Sekonda. I replaced the battery after taking off the back. Very hard to replace the back What I did was to mark the position of the winder groove to make placing it easier. I then got a G- clamp. The type that works similar to a sealant gun. It has nylon pads on it. I placed the watch face down on a formica covered worktop, then got the clamp put one end under the table and the other on the watch back. Nothing was touching the watch glass. A few pumps of the lever and the back popped onto place.

I used a special press http://www.findingking.com/p-29864-case-crystal-press-13pcs.aspx it was still rock solid to get on even with the press, i pressed down hard on it and had to hit the tip of the handle with a hammer whether it was blind or beginners luck it went on, i also noticed that the back of the case was bending in over so i placed the case on the press and pushed it out a bit, its at this point that it went on, i have to say i am not looking forward to doing it again, when this battery runs out

I needed to change the battery and used a Swiss Army knife blade to gently spring off the back cover using the small metal lip that is provided. I used tweezers to remove and replace the small battery. That was the easy part! Getting the back replaced was difficult. I used the tip from the post above about using a G-Clamp but modified it to use a Kreg clamp with furniture felt pads to protect the watch from scratches, plus visegrips to add extra force. Here's the sequence of steps I used: First, I put the back cover into the refrigerator freezer compartment for 30 minutes to cool it down to -6 degrees to hopefully shrink it a tiny bit. I did this because it seemed oversized and would not even half seat itself. I got it out of the freezer and then quickly aligned the winder notch and then carefully placed the watch and its cover between two 1" diameter furniture felt pads. Then I took the Kreg clamp with its flat circular clamp faces and squeezed the felt pads and watch to hold the assembly firmly in place and partially seat the back. Then I used the visegrips to squeeze the Kreg metal clamp faces at the spot where the back was still raised a bit (approximately one third of the circumference). And miraculously the back cover snapped into place without doing any physical damage to the watch. As others have commented, I'm sure hoping this new battery lasts a while because I spent three hours of trial and error to find this solution and I can't tell if I just got lucky !