Much like a metal bracelet that starts off at its longest, your rubber strap starts long and is designed to be adjusted to fit.
Allow yourself plenty of time, and try your watch and strap on your wrist before you start cutting to work out how much to shorten the strap by.
Having looked at the strap length on your wrist, if you need to shorten the strap, take the watch off, place it on a soft surface and remove one strap end from the buckle using the pointed tool (included) to push into the holes in the sides of the buckle to release the spring bar. Be careful not to lose the spring bar.
With a sharp knife or scissors, carefully cut just one section from the free end, cutting neatly and carefully along the centre of the first guide groove on the inner surface of the strap at the end nearest the buckle. Don't be tempted to cut two sections at once.
Now refit the strap end back into the buckle depressing the spring bar to locate into the hole position nearest the centre join of the buckle. Use your fingernail or a spring bar tool if you have one.
Now try the strap on your wrist again - it’s surprising how much removing just one rubber section changes the size.
If the strap still needs to be smaller, repeat the above steps, alternating which side you cut down until the strap is the perfect length.
Each time, re-attach the strap using the holes nearest the centre of the buckle so you can always increase the size a little just in case.
The attachment holes in the buckle are half the length of the strap sections so if you end up a tad too tight or a tad too loose, adjust which set of holes the strap attaches to in the buckle until it’s perfect.
It pays to be patient so you don't end up cutting your strap too short. Remember as your body temperature increases, your wrist size will increase too.