Time Machine

how do I switch my external drive to backup a new macbook instead of the old one?

When I transferred data from a backup of the old machine (macbook Pro 2009), the new machine (macbook air 2021) got named the same name as the old machine... a little confusing, but time machine seems to know the difference. The external hard drive is full of old backups of the old machine. Can I just delete all but the most recent to make space? I would really prefer to have them treated a separate machines, since I will be using the old machine for limited purposes going forward.d