List the row of dataframe/attributes in combobox

    Hii I am new to qgis plugin creation.I have create a`enter code here` 3 Combobox like these Combobox,Combobox_1,Combobox_2, I get the data input from Combobox

using the lines

layers = QgsProject.instance().layerTreeRoot().children()
self.dlg.comboBox.addItems([layer.name() for layer in layers]) 

   I stucked here itself.Now I need to selected the listed layer from Combobox.Then to list the index of the dataframe in Combobox_1,Combobox_2 which from the Combobox.

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enter image description here

For example I get the input as per above image through Combobox then I need to list Well_no Latitude Longitude Years EC_GEN like these in Combobox_1,Combobox_2. pls give ur suggestions...