Hi,
Replacement watchbands are available online.
Here’s a link to just one [https://www.aliexpress.com/item/Stainless-Steel-Watchband-24mm-for-Sony-Smartwatch-2-SW2-Replacement-Band-Smart-Watch-Strap-Bracelet-Black/32660712246.html|supplier]. It is shown only to give an idea of the cost of the watchband. There are other suppliers that may suit you better. Just search for ''Sony Smart Watch SW2 watchband'' to get results for suppliers of the part.