Update multiple records in table 2 from the customer's statute from table 1

Hello !

I'm sure it's very simple but I need some help because I'm trying several ways to do this without success at all...

I'm trying to do that :

I'm in the same base but I've 2 tables, one for customer list and one for machines list. Both are sync from another base.

- In table 1, when I pass the customer's statute to "completed", I would like, in table 2, all the statuses of the client's machines to change to "completed" too.

For example, when I pass the X customer to "completed" in table 1, all the X customer's machines in table 2 pass to "completed". 

Most of errors that I had was "record doesn't exist" or "invalid input"...

Thanks a lot !