Sharepoint LookUp Column Advice

Hello,

I'm hoping someone can point me in the right direction.

I  have the following 2 SharePoint Lists:

• Postcode Uplift (2 columns) - this contains 575747 postcodes in Column - Postcodes, and their corresponding Uplift factors within Column - Uplift 

• Learner Lists - I use an Excel Table to upload learner information to this list which includes postcode.

I'd like to link the Learner List so that when I upload a learner, an Uplift column is automatically filled with the corresponding Uplift Factor.

I've managed to create the link via a Postcode column in Learner List set as a LookUp, however - I can't then manually add postcodes, or use a flow to upload the data, as I then appear to have to select the postcode from a drop down list when entering a new learner onto the learner list.

As there are so many postcodes to search, this would take too much time to have to scroll to find the correct postcode.

Is there a way of uploading the learner to the List & then for the Uplift column to complete the Uplift Factor?

Thank you 

Lisa