How to create connection between database

Hello , i have an issue. i’have like two huge database and i can not update them myself. so i wanted to create a database for members. and connect each members to a specifique row on my database to update the information. i do not know how to do it.
like collection A is the information and collection B the owners of the informations, how to connect both

thanks

Hi,
Have you heard about reference fields ?

Roi.