The errors: W and V are interchanged, B and V are interchanged (Spanish speakers)
The Quick Fix: W: round lips, no teeth; V: upper teeth touch lower lip, sound continues
How to Practice: work on making w, v and b distinct from each other, practice common words with w and v, select a target word, repeated phrase practice
Resources:
website links: https://www.speechmodification.com/free/w-and-v
https://www.speechmodification.com/free/american-accent-error-patterns-v-for-w
resources: w and v practice video (below) https://youtu.be/629CgIrYAzo