Trying to mass update records in subgrid

I'm using Dynamics on premise 2016 and one field in my associated products for an order was originally set as a number field, however now it needs to change to a text field. I've added a new text field and was hoping to export the list out (which worked fine) and reimport the changes when I copy/paste the old data into the new field. Problem is, there's no import feature when looking at the Associated Products sub grid. Any hints to make this work, or instead, anyway to change the field from a number value to a text value? Either way is fine with me.