Automatically append new json Data to my existing dataset and Queries

Hey Community, 

im quite new to the BI-Area so maybe I am not using the perfect wording.

I have a report in Power-BI. I partly use csv. files and for another part I am using json Data from a Rest Api.

I already transformed the json data according to my needs in Power query. 

But still some problems remain.

The  filter in the rest api is filtering for data, e.g. all entries for the month March. When the filter is changed in the next months to April, I would like to append the new json data to my existing data, so i have the combined data for both months.

How could I execute this in Power Query/M so the new data gets automatically appended to the existing query?

Also I would like to have a button or a field where a user can fetch the new/updated data from the rest api.

When Im changing the filter in the rest api, the URL for the json changes, therefore It will make a new query. I hope this is understandable. If you need any more information please let me know