Comments - Access to more databases

This sounds like a connection definition problem. You should be using two different connections, one per database. When building your queries, you should be referencing the database connection for the database you want to query.

Example:

$cnn_db1 = mysqli_connect($Servername, $Username, $Password, $Database1);
$cnn_db2 = mysqli_connect($Servername, $Username, $Password, $Database2);
$rst_query1 = mysqli_query($cnn_db1, "SELECT * FROM Users")
$rst_query2 = mysqli_query($cnn_db2, "SELECT * FROM Users")
mysqli_free_result($rst_query1);
mysqli_free_result($rst_query2);
mysqli_close($cnn_db2);
mysqli_close($cnn_db1);