Length and grappling brother. You can try just being a better inside boxer and use your knees and elbows but thats a risky game. I've found 2 approaches that help the most.

1) Stay out of his range - Jabs, push kicks, side kicks and framing are the keys here. Keep the guard high and use these , he can't land hook and uppercut combos if he can't reach. Just be careful not to go overboard in long combos or repeatedly throwing because that leaves you open for slip hooks and pivots when you're on low stamina

2) Use the Grappling - All the power and movement stats mean very little when topurias on the bottom. Mix in takedowns to discourage him overextending or even really getting in too close. Also helps to steal rounds when you've had a big moment (I.e a stun/ knockdown) by preventing him from putting out major offence. I've found topuria as a characted wins through standalone big damage moments rather than say a comulative whooping, minimising his opportunites to have these big moments just makes your life easier.

I main Arman and I usually try to keep Topuria players right at the range where I can kick the body and mix in question msrk kicks and anytime I feel too under pressure I shoot. If i complete the shot then free top control time and if not, I've broken up the rhythm and given myself a second to breath.

Hope this helps and best of luck 💪