I am building an edit form which needs to update values on fields based on the inputs when you hit submit. The form updates the fields successfully for any lightning-input-fields, but I need to do it for a picklist as well. I have tried with both a combobox and select and have had no success. The field is of type long text.
There was a similar issue asked here and I have attempted to use the answer given, but it didn't work for me. 
The onChange successfully updates this.value to the correct values (seen in console.log), but when trying to update the Value__c field to that value, it doesn't work. How can I get it populate to and update the field?

this.valueconsole statement in your submit showing the correct value?