Step-by-Step Guide
Log in to Admin Panel
Access your Magento 2 backend by logging in with your credentials.
Navigate to Content
In the left-hand menu, go to Content > Design > Configuration.
Select the Store View
On the Configuration page, you will see a list of your store views. Click on the Edit button next to the store view where you want to change the theme.
Change the Theme
In the Applied Theme section, use the dropdown to select your new theme.
Save the Changes
After selecting the theme, click the Save Configuration button in the upper-right corner.
Flush Cache
After saving, clear your cache by navigating to System > Tools > Cache Management, then select all caches and click Flush Magento Cache.
Result
Your new theme should now be applied to your selected store view.
Let me know if you need further assistance!