After removing original watch band by depressing spring bars with a proper tool, use masking tape to protect watch lug surface.
And then install spring bars back to watch.
Thread the long end of the strap through the top spring bar gap of your watch at the 12 o’clock position so the buckle is at 12 o'clock.
Then through the spring bar at 6 o'clock. Take that same long part of the watch strap back through the keeper. Pull it through.
Shift the watch case up or down to ensure it is centered between the keepers and it sits properly on your wrist.
Equidistantly move the watch between two keepers. Finished.