Runtastic / Garmin data import

Hello, I'd like to ask you for the help related to the data export/import. I have downloaded my data (export) from the runtastic and now I need to import it to the garmin connect. Could you help me please how to do it? I have tried to connect the garmin account in the mobile adidas running (formely runtastic) but it doesn't work.I still couldn't see any old activitities in the Garmin app. Just in runtastic :(. The downloaded data is in the json format, that is not possible to import in garmin web app. Thanks in advance.
M.