Insert a lookup field in subform based on a text field on the mainform

Insert a lookup field in subform based on a text field on the mainform

I have the following:
Mainform: MOA_Details
Text field: MOA_Partners

Subform: Airstrips
Lookup field: MOA_Partners

I would like to have the lookup field in Airstrips subform populated with the same item typed into the text field in MOA_Details mainform.

Please advise how its done.