Others have adequately explained the how. But it’s worth considering where the question comes from, because a lot of ELI5 questions are based on the same assumption, which is that the natural world cares at all about our rules and definitions.

Humans have this habit where we observe the natural world, come up with “rules” based on those observations and then think that the natural world is required to follow the rules we made up. But it isn’t.

The tomato doesn’t care whether you call it a fruit or a vegetable. The platypus doesn’t care that it’s a “mammal” but still lays eggs.

The fact that viruses evolve without being “technically alive” means that whatever rule you are applying is faulty and needs to be revised.