Dog 'Attacked' me 3 times, drew blood. Where do I go from here?

Sorry but basically my dog has bit me and drew blood 3 times. They all had triggers but I don't know where to go from here, we were able to manage really well by mitigating having food or anything he shouldn't have access to away and secure but recently we've been with our younger sister who doesn't care whatsoever.

My dog managed to get a packet of digestives and i intervened by holding his collar so he couldnt eat them and just hold them, i tried to trade up with a treat but he saw the biscuits as higher value and had no interest whatsoever. after he dropped the biscuits he got aggressive and bit my forearm 4 times as i held his collar with minimal force, i never thrashed or pulled away I just took the 4 bites then put him in the garden to chill out while i cleaned up the chocolate.

The issue is this is the 3rd time it's happened and its always in regards to an item he cant have, i believe its resource guarding but i can take his food bowl and stroke him but he doesnt care, so its items he believes im going to take. It's always traded up but recently he's drew blood on me twice with multiple bites into my forearm. I don't feel safe having him with this behaviour with a young child who clearly doesn't care about the situation, if he was to bite her the way he has me it would be scarring, I'm just really struggling to navigate this situation and don't know where to go from here, he's still cuddly and affectionate but when it comes to items like chocolates or dangerous items he will escalate but I can't just leave him to eat a packet of digestives so I have to trade up or wait for him to drop it.

I understand there's not much that can be said but I just need access to good resources or to navigate this situation, the 'attacks' are becoming more common with multiple lunges, i believe they're all surface level but theres puncture wounds i can't discern the severity of, he hasn't thrashed or shook my arm just bit then let go then bit again, i cannot remember if he held my arm or not. I can't judge it based on pain due to a tolerance I have which doesn't allow me to recognise injuries.

Final Note: On the Dunbar Bite Scale I can't tell if it's level 3.5 attacks or level 5 because its multiple wounds but its not bleeding profusely or crazy I just have holes down my arms.

Sorry really struggling and need help, he will be muzzled on walks from now on.