The point of using transaction is to be able to execute multiple statements (insert, delete, update) and then commit changes or roll everything back in case of error.
You may use transaction to update single table but in your case I don't much point in it since it appears that both tables relate on ID (id=7).
So, what I would do is to use single transaction to update both tables:
Code:
Option Explicit

Private Sub cmbSumit()
On Error GoTo ErrHandler

    Conn.BeginTrans
    Conn.Excute "update H1 set Fname = 'City1' where FieldID=7"
    Conn.Excute "update D1 set name = 'Ram' where FieldID=7"
    Conn.CommitTrans
    
    Exit Sub
    
ErrHandler:

    MsgBox Err.Description
    Conn.RollbackTrans
    Err.Clear

End Sub