It’s possible to change your own watch strap at home.
Start by finding a clean, flat surface. Lay down a soft cloth so that you don’t scratch your watch face while you’re changing out your strap. Then, lay your watch down on its face so you can see the back, unbuckling it so the current buckle lies flat.
Then, orient yourself with your new watch strap.
Your new strap comes in two pieces. The shorter piece will have the buckle attached, while the longer piece has holes in it to attach to the buckled piece. Lay these pieces underneath the same types of pieces on your existing watch strap so they’re parallel. This will help you fasten the new strap to the correct sides of your watch.
Next, you need to remove your old watch strap. Most straps are attached to watches using a telescoping, spring-loaded bar. Use a spring bar tool to maneuver these spring bars out of the watch strap. Make sure you have some sort of barrier set up; because spring bars are spring-loaded, they can easily fly off in any direction, and can quickly get lost in shaggy carpets or down vents.
Finally, place the spring bars in the replacement straps. Insert the bottom part of a spring bar into your watch face, then push on the top to telescope it into place. When you maneuver your strap into place and remove your spring bar tool, the telescoping spring bar should snap into place.
Do this to both sides of your strap, and you will have installed your new watch strap.