Detta besvarades i en Sage Advice-artikel (du hittar den i Sage Advice-kompendiet).
Q: Can a bonus action be used as an action or vice versa? For example, can a bard use a bonus action to grant a Bardic Inspiration die and an action to cast healing word?
A: No. Actions and bonus actions aren't interchangeable. In the example, the bard could use Bardic Inspiration or healing word on a turn, but not both.