It's always a good practice to not set internal stuff in one component from another component directly.
Instead, add a sub to the activity, such as:
B4X:
Sub SetStat(text as string)
lblSTAT.Text = "Hello world"
End Sub
Then, use CallSubDelayed as Erel suggested to call that sub. That way, you'll get all the external connections properly documented, which is a godsend when you start changing stuff a month later...