Why is the left bud not connecting with phone only right works

Firstly — attempting to repair your earbuds is an endeavor, and companies like Google and Apple want to make earbuds essentially disposable. If the earbud cannot charge or indicate any signs of life, it is possible that the battery is dead. All earbud repairs are difficult and risky for the circuitry and plastic structure. However, if you want to try opening the earbud, try heating the plastic with a heat gun (or hairdryer) and slowly prying at the gaps between the plastic. Here is teardown for your earbuds: Google Pixel Buds 2 Teardown

If the bluetooth circuitry is damaged, it is likely unrepairable/unreplaceable.