Ah I see, I think a simple way that you do is, manually create a simple dropdown field (put a value) as example:
https://take.ms/Vyqzf
Once you have save the custom field, it will add the custom field data in
#__easyblog_fields table (
https://take.ms/pytVG )
As you see, the options column is where the values is store (in json format).
By here, you can alter your .txt file to have this format. example below:
[{"title":"10","value":"10"},{"title":"20","value":"20"}]
And you can change the options columns for that specific dropdown field in the
#__easyblog_fields table (
https://take.ms/el6IN )
*p/s: you are suggested to backup your database, for precaution step