I can't find these instructions anywhere online - so I hope these notes help!
The AS302P SMETS2 has two buttons. I've labelled the top button A and the bottom button B.
Press the A button once to bring up the menu. The display should light up. It should show "General".
Press the B button. This scrolls down the display. Press it a couple of times until it says "Registers". If you go past it, press it again and again until Registers scrolls back into view.
Press the A button to enter the Registers menu. It should show the word "Cumulative".
Press the A button to enter the Cumulative menu. It should show your "Import".
Press the B button once to scroll down. This should show you your "Export".
This "Cum. Exp." figure is what you give to your energy provider when they ask for your solar export readings.
If that doesn't help, you can read the AS302P manual.
(And, yes, your energy provider should really be able to read these automatically. That's the whole frickin' point of a smart meter!)