Update Text Field from Gallery Button

[cmegow]

I would like to update the text field "PO Number" with the "PO#" in the item selected in the in the gallery when the arrow button is clicked.  How do I do this?

Please provide formula for Text Field "PO Number" and Formula for OnSelect for the Button.

Both fields are Single Line of Text Fields.

Thank you for your help!!!

[cmegow]

UpdateContext({TheVar3: ThisItem.'Project Name'.Value})

This formula did the trick for the lookup field.

This app is DONE!

Thank you for all your help @v-bofeng-msft