Hi Trang,
Thanks for posting in our forum.
I go through the post carefully, per the description, it seems that you want to update the training time in B list if the status column is changed/edited in A list. If so, the demand can only be realized using Flow as there has no out-of-box feature in SharePoint Online.
However, as the category here is not on Microsoft Power Automate which focus on using Flows to work with SharePoint list better and engineers here have limited resources on testing flows. To make sure you could get dedicated help on building flows in Microsoft Power Automate, I would sincerely suggest you post in Microsoft Power Automate Community which is a dedicated channel for Power Automate related questions. Members and engineers there are more professional on such questions, you may have better experience there.
Also, I found some threads in Power Automate Community and hope they could offer a bit ideas on your scenario.
Solved: Update item column - Power Platform Community (microsoft.com)
Solved: How to update field column when item list has chan... - Power Platform Community (microsoft.com)
Solved: Change specific column when a column has changed i... - Power Platform Community (microsoft.com)
How to update a sharepointlist item when a seconda... - Power Platform Community (microsoft.com)
Thanks for your understanding and hope your concern could get resolved perfectly in related community.
Best Regards,
Mia