Web.config file in D365 FO

 Go to :

K:\AosService\WebRoot

look for web.config file

search for following

<add key="DataAccess.Database"

<add key="DataAccess.DbServer"

<add key="DataAccess.SqlPwd"

<add key="DataAccess.SqlUser"

These are for DB, Server, and SQL password and SQL User

Microsoft

Link