For the first bit, start here and modify the content to meet the specific requirements of research into the impacts of Covid:
https://brandongaille.com/12-case-study-method-advantages-and-disadvantages/
(OR simply use your lecture notes, which ought to tell you much the same thing).
For the second bit, you're going to need to identify two commercial organisations
in your own country (which I suspect might not be the UK, where this website is based) that operate in very different sectors (and thus where the impacts of Covid might be very different). For example, if you're in India, Big Bazaar operates in the retail sector, whereas Tech Mahindra is in the field of technology. You'll then need to contact senior executives within those companies to seek their assistance and structure interviews to elicit the relevant responses. (In practice it might be far easier to contact, say, the owners of a local chain of restaurants and of a local plumbing business. All that really matters is that the businesses are large enough to employ a reasonable number of people and that they operate in totally different sectors).
BTW: You might point out to whoever set you this task that it would be better if he/she used up-to-date data. The number of reported deaths from Covid (as counted by WHO) is approaching 6.5 million but many analysts believe that the real total is actually closer to 15 million.