What he needs to do is twofold - firstly start ask questions about important things that aren't being discussed and for which the government isn't prepared - things like how we protect ourselves in future from subsequent waves of this (or other potential pandemics), what capacity they are going to require in the NHS, or what relief they are going to offer business after this is all over, or whether (to use a good point raised on here, sorry but I can't remember who said it) whether he is going to seek democratic consent if he gives away sovereignty in any new trade deals.
Secondly, he needs to bin off many of his advisors and replace them with people who actually know what they are talking about. Like Corbyn did (and Miliband, Brown and Blair) he's surrounded himself with political advisors, which is sort of pointless to him because they'll only ever tell him things he already knows. What he needs are people who can tell him that the government's statements are wrong, or their plans are a bad idea, and why - he already has suitable candidates as MPs so it shouldn't be that hard.