To take the opportunity to, taking the occasion to, on the occasion of.
Long explanation:
The grammar point Noun を機にして (wo ki ni shite) is used to express the idea of taking a certain event or situation as an opportunity to do something else. It is often used in contexts where a change of situation or environment leads to a different action or state. In other words, it means 'taking the occasion of', 'on the occasion of' or 'to take the opportunity to'