Steps to fix it:

• Reset the phone:-Occasionally, the issue is trivial, and a simple restart will resolve it. So, before you go looking for alternative options, try rebooting your device and seeing if it helps.
• Verify the internet connection Try opening a webpage in a browser on your phone because Google needs to get the results from the internet. If that doesn't work either, the issue is most likely with your internet connection. Restart your modem if you're using Wi-Fi. Switching between Wi-Fi and mobile data is also a good idea.
• Add the search widget again-If the issue is limited to the search bar or the search widget, consider re-adding it. Delete the widget by holding it down and dragging it to the remove icon. Then, on the home screen, tap and hold an empty area and select Widgets from the options. Look for Google search bar. It will appear on the home screen if you drag it there.
• Clear the app cache:-Many people have found that clearing the cache for the Google app is beneficial. To do so, navigate to Settings > Apps/Application Manager > Google and  After that, touch on Storage, then Clear Cache.

Read More: Why did Google search stop working? How can I fix it?