上任 (shàng rèn): Take up an official post (Verb) — Meaning & Stroke Order

Upon taking office, the new mayor immediately began to promote comprehensive reform of the city's transportation system.

Do you think there will be any changes to our workflow after the new director takes office?

After the new principal took office, the school became better.

After taking office, he not only failed to fulfill his promises but also further lowered team morale.