You can't I'm afraid, the router and points will update themselves to the new firmware when it's pushed out to them by Google/Nest. Sometimes restarting your points will kick this process off but there's no guarantee, the firmware is being rolled out progressively throughout April. I haven't received the updates as yet either.
FYI, the Google Wifi app has been discontinued, Google Home should be used for all wifi management going forward.
The latest firmware release is going out to devices now. Everyone will have it within the next couple of weeks, but some may have already received it. If you haven't seen the update on your device yet, just give it a bit more time and it will eventually download and install.
Just to give a bit more info, the update version for both Google WiFi and Nest WiFi will be 14150.43.80. If you are seeing a different version number when you check in Google Home, you have yet to receive the updated firmware. Let me know if you have any questions about that.